BEIRUT -- A look at the reasons for and possible implications of the escalation of Israel's involvement in Syria's civil war.

WHY NOW?

Israel has said repeatedly it does not want to get dragged into Syria's civil war but has also warned that it will not allow so-called "game-changing" sophisticated weapons to flow across the border to Lebanon's Hezbollah, an Islamic militant group allied with the Syrian regime.

Israeli defense officials believe Iran has stepped up shipments of weapons to Hezbollah through Syria, including accurate longer-range Iranian missiles, as President Bashar Assad's position weakens. This could help explain the back-to-back Israeli strikes on Friday and Sunday on alleged Hezbollah-bound weapons in Syria. Before this week, Israel aircraft had struck Syria only once, in January.

Analyst Paul Salem of the Carnegie Middle East Center in Beirut says Israel may simply be sending a stern warning to deter such weapons smuggling. Salem says Israel also appears to be increasingly concerned about Iranian and Hezbollah forces fighting alongside Assad's troops, close to Israel's borders.

WHAT IS THE U.S. VIEW?

White House spokesman Josh Earnest said Sunday that "Israelis are justifiably concerned about the threat posed by Hezbollah obtaining advanced weapons systems, including some long-range missiles."

President Barack Obama said the U.S. coordinates closely with Israel, implying that Washington was not taken by surprise by the Israeli strikes.

The U.S. has long resisted getting involved in the conflict amid concerns that foreign weapons could end up in the hands of al-Qaida-linked groups or other extremists fighting with the rebels. However, Defense Secretary Chuck Hagel said recently that Washington is reviewing its opposition to arming the opposition.

The Israeli strikes illustrate that Obama and Israeli Prime Minister Benjamin Netanyahu have drawn different red lines in Syria's conflict.

Israel's main concern is that Hezbollah could obtain advanced weapons.

Obama has warned that the use of chemical weapons by the regime could have "enormous consequences." There have been some indications of chemical weapons use, but Obama has said he needs more definitive proof before making a decision about how to respond.

COULD THIS ESCALATE INTO A WIDER MIDEAST WAR?

Israel, which commands the region's most powerful military, appears to be taking a calculated risk that Syria, Hezbollah or Iran won't retaliate for its air raids.

If the trio were to do so, it would mean opening up a new front at a time when it is fighting for the Assad regime's survival. Hezbollah also risks losing its position as the dominant military and political power in Lebanon, something it painstakingly rebuilt after the 2006 war, if Israel were dragged in to the conflict.

The initial Syrian response to Israel's airstrike early Sunday appeared relatively muted. Syria's government called the attacks a "flagrant violation of international law" and warned it has the right "to defend its people by all available means."

Still, Israeli officials have signaled Israel will not stop blocking weapons shipments to Hezbollah, raising the possibility of more Israeli airstrikes and a further escalation. Salman Shaikh of the Brookings Doha Center in Qatar says the Assad regime, Hezbollah and Iran increasingly view the Syria conflict as a zero-sum game.

WHAT IS IRAN'S ROLE?

Iran is the senior partner in the axis since it supports the Assad regime and Hezbollah with weapons, though it's not clear how much tactical sway is being exerted by Tehran.

Advisers from Iran's Revolutionary Guard are believed to have longtime roles in Hezbollah's militia forces and Assad's army – serving as both point men for Tehran's aid and liaisons with the ruling clerics in Tehran. Yet Iran also keeps a distance from the actual battlefield.

Gen. Masoud Jazayeri, assistant to the Iranian chief-of-staff, told Iran's state-run Arabic-language Al-Alam TV on Sunday that Tehran "will not allow the enemy (Israel) to harm the security of the region" and that "the resistance will retaliate against the Israeli aggression against Syria."

Iran would have a major say in any decision to retaliate for the airstrikes but is not believed to have an appetite for a confrontation with Israel. While Iran is fighting for regional influence and has often used its anti-Israel stance to do so, it has never attacked the Jewish state.

WILL THE ISRAELI STRIKES CHANGE THE COURSE OF SYRIA'S CIVIL WAR?

The uprising against Assad erupted in March 2011 and quickly evolved into a civil war, leaving tens of thousands dead and millions displaced. Assad and those trying to topple him remain locked in a battlefield stalemate, with neither side able to deliver a decisive blow.

The rebels are dominated by Syria's Sunni Muslim majority, while Assad is a member of the Alawite sect, an offshoot of Shiite Islam. He as rallied hardcore supporters around him, including members of Syria's ethnic and religious minorities who prefer the current regime to Sunni majority rule.

During four decades of rule, Assad and his father and predecessor, Hafez, used Syria's staunchly anti-Israel positions as a source of legitimacy even though both men kept Syria's frontier with the Jewish state quiet.

Syria's civil war has increasingly eroded Assad's anti-Israel "credentials," after the regime attacked Palestinian refugee camps in Syria and the Palestinian militant group Hamas, made up of Sunnis, broke with the regime because of its crackdown on the rebels.

If Assad does not retaliate for the latest Israeli strikes, his claims to anti-Israel militancy would become even more tenuous. In an attempt to deflect attention, Syrian government officials on Sunday tried to portray the Syrian opposition as engaged in a common cause with Israel.

Future Israeli air attacks could also wipe out key Syrian military installations. Rebel forces have managed to seize a number of Syrian military bases, seizing heavier weapons but have advanced only slowly because of the regime's air superiority.

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Associated Press writer Brian Murphy in Dubai, United Arab Emirates, contributed reporting.

Earlier on HuffPost:

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  • This Friday, March 1, 2013 file citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, shows a Syrian child, injured by heavy bombing from military warplanes, in the town of Hanano in Aleppo, Syria. (AP Photo/Aleppo Media Center AMC, File)

  • In this Monday, March 4, 2013 file image taken from video obtained from Ugarit News, which has been authenticated based on its contents and other AP reporting, a statue of former Syrian President Hafez Assad is pulled down in a central square in Raqqa, Syria. (AP Photo/Ugarit News via AP video, File)

  • In this Tuesday, March. 5, 2013 file citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, shows a Syrian man sitting on a fallen statue of former Syrian President Hafez Assad in a central square in Raqqa, Syria. (AP Photo/Aleppo Media Center AMC, File)

  • Smoke rises following an explosion in the Syrian village of Jamlah in the southern province of Daraa, Syria, seen from the Israeli-controlled Golan Heights ,Thursday, March 7, 2013. (AP Photo/Ariel Schalit)

  • This file citizen journalism image taken on, Sunday, March. 10, 2013 and provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, shows Syrians standing next to dead bodies that have been pulled from the river near Aleppo's Bustan al-Qasr neighborhood, Syria. (AP Photo/Aleppo Media Center AMC, File)

  • Syrian rebels aim their weapons as they take position in a building during clashes with regime forces in the Salaheddine district of Aleppo in northern Syria on March 16, 2013. (JM LOPEZ/AFP/Getty Images)

  • Syrian rebels raise their weapons under a pre-Baath Syrian flag currently used by the opposition during an anti-regime protest in the northern city of Aleppo on March 22, 2013. (BULENT KILIC/AFP/Getty Images)

  • The coffins of Sunni Muslim cleric Mohamed Saeed al-Bouti and his grandson Ahmed al-Bouti, who both died in a suicide bomb attack, are carried during their funeral ceremony on March 23, 2013 at the Omayyad mosque in Damascus, Syria. (LOUAI BESHARA/AFP/Getty Images)

  • People mourn during the funeral ceremony of Sunni Muslim cleric Mohamed Saeed al-Bouti, who died in a suicide bomb attack, on March 23, 2013 at the Omayyad mosque in Damascus. (LOUAI BESHARA/AFP/Getty Images)

  • Grand Mufti of Syria Ahmad Badr al-Din Hassoun (L) takes part in the funeral ceremony of Sunni Muslim cleric Mohamed Saeed al-Bouti, who died in a suicide bomb attack, on March 23, 2013 at the Omayyad mosque in Damascus. (LOUAI BESHARA/AFP/Getty Images)

  • People pray in the Omayyad mosque courtyard during the funeral ceremony of Sunni Muslim cleric Mohamed Saeed al-Bouti, who died in a suicide bomb attack, on March 23, 2013 in the Syrian capital Damascus. (LOUAI BESHARA/AFP/Getty Images)

  • A rebel fighter fires towards Syrian government forces positions from a building in Saif al-Dawla district in the northern Syrian city of Aleppo on March 25, 2013. (BULENT KILIC/AFP/Getty Images)

  • A Rebel scouts the positions of Syrian government forces at Saif al-Dawla district in the northern Syrian city of Aleppo on March 23, 2013. (BULENT KILIC/AFP/Getty Images)

  • Rebels clash with Syrian government forces at Saif al-Dawla district in the northern Syrian city of Aleppo on March 23, 2013. (BULENT KILIC/AFP/Getty Images)

  • In this Monday March 25, 2013, citizen journalism image provided by Aleppo Media Center AMC which has been authenticated based on its contents and other AP reporting, anti-Syrian regime protesters burn a portrait for Syrian President Bashar Assad during a protest, in Aleppo, Syria. The Arabic on the poster reads, the dog of Iran." (AP Photo/Aleppo Media Center, AMC)

  • An rebel sniper aims at Syrian government forces positions from a hall in Saif al-Dawla district in the northern Syrian city of Aleppo on March 25, 2013. (BULENT KILIC/AFP/Getty Images)

  • In this Sunday, March 24, 2013 image taken from video obtained from the Ugarit News, which has been authenticated based on its contents and other AP reporting, Free Syrian Army fighters drops a shell into a firing tube, in Damascus countryside, Syria. (AP Photo/Ugarit News via AP video)

  • In this image taken from video obtained from the Ugarit News, which has been authenticated based on its contents and other AP reporting, Free Syrian Army fighters aim their weapons during clashes, in Damascus countryside, Syria on Monday, March 25, 2013. (AP Photo/Ugarit News via AP video)

  • In this Thursday March 28, 2013 image taken from video obtained from the Ugarit News, which has been authenticated based on its contents and other AP reporting, shows a building at the Syrian government checkpoint on fire, in Dael less than 15 kilometers (10 miles) from the Jordanian border in Daraa province, Syria. Thursday, March 28, 2013. (AP Photo/Ugarit News via AP video)

  • In this Thursday March 28, 2013 image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, shows fighters from the Syrian Free Army firing on a Syrian army position in Dael less than 15 kilometers (10 miles) from the Jordanian border in Daraa province, Syria. Syrian rebels on Friday captured a strategic town near the border with Jordan after a day of fierce clashes that killed at least 38 people, activists said, as opposition fighters expand their presence in the south, considered a gateway to Damascus.(AP Photo/Shaam News Network via AP video)

  • In this Thursday March 28, 2013 image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, shows Syrian Free Army fighters in Dael less than 15 kilometers (10 miles) from the Jordanian border in Daraa province, Syria. (AP Photo/Shaam News Network via AP video)

  • In this image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, smoke rises from buildings due to shelling in Damascus, Syria, on Thursday, March 28, 2013. (AP Photo/Shaam News Network via AP video)

  • In this photo released by the Syrian official news agency SANA, plastic tables and chairs turned upside down, are seen on the floor of the open-air cafeteria at Damascus University in the central Baramkeh district, in Damascus, Syria, Thursday, March 28, 2013. (AP Photo/SANA)

  • In this image taken from video obtained from the Shaam News Network, which has been authenticated based on its contents and other AP reporting, a dead body lays on a street due to heavy fighting between Free Syrian Army fighters and government forces in Damascus, Syria, on Thursday, March 28, 2013. (AP Photo/Shaam News Network via AP video)

  • This citizen journalism image provided by The Syrian Revolution which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding a banner and Syrian revolution flags, during a demonstration in the town of Haas in the northwestern province of Idlib, Syria, Friday, March. 29, 2013. The banner in Arabic reads: "We will continue despite killing us. We will continue although we were betrayed. We will continue and God is with us. Good news to those who are patient." (AP Photo/The Syrian Revolution)

  • This citizen journalism image provided by Edlib News Network, ENN, which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding a placard, during a demonstration, in the town of Kafr Nabil, Idlib province, northern Syria, Friday, March. 29, 2013. (AP Photo/Edlib News Network ENN)

  • This citizen journalism image provided by Edlib News Network, ENN, which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding a placard, during a demonstration in the town of Haas in the northwestern province of Idlib, Syria, Friday, March. 29, 2013. (AP Photo/Edlib News Network ENN)

  • This citizen journalism image provided by The Syrian Revolution which has been authenticated based on its contents and other AP reporting, shows anti-Syrian regime protesters holding banners and Syrian revolution flags, during a demonstration in the neighborhood of Bustan Al-Qasr in Aleppo, Syria, Friday, March. 29, 2013. (AP Photo/The Syrian Revolution)