BEIRUT — Lebanon's prime minister resigned Friday due to government infighting that threatens to leave a void in the state's highest ranks at a time of rising tensions and sporadic violence enflamed by the civil war in neighboring Syria.

Najib Mikati stepped down to protest the parliament's inability to agree on a law to govern elections set for later this year, as well as for the Cabinet's refusal to extend the tenure of the country's police chief, who is about to retire.

Underpinning the political crisis are Lebanon's hugely sectarian politics and the fact that the country's two largest political blocs support opposite sides in Syria's civil war. Lebanon and Syria share a complex network of political and sectarian ties, and many fear that violence in Syria will spread to Lebanon.

In a speech aired live Friday on Lebanese TV, Mikati said he hoped his departure would force other politicians to find solutions.

"Today I announce the government's resignation, hoping that God willing it will provide an impetus for the primary political blocs in Lebanon to assume their responsibilities," he said.

"There is no way to be loyal to Lebanon and protect it other than through dialogue that opens the way to the formation of a salvation government that represents all Lebanese political powers and takes responsibility for saving the nation," he said.

There were signs of rising tensions before Mikati's speech.

Gunmen who support and oppose Syrian President Bashar Assad clashed Friday in the northern Lebanese city of Tripoli, leaving six people dead and more than 20 wounded, according to state-run National News Agency. Clashes between the Sunni neighborhood of Bab Tabbaneh, which supports Syria's rebels, and the adjacent Alawite neighborhood of Jabal Mohsen, which supports Assad, have broken out repeatedly in recent months.

Also in Tripoli, the Lebanese army said a soldier was killed and several others wounded during an army raid to capture several gunmen.

Mikati's resignation follows months of political wrangling in the Lebanese parliament that has yet to agree on a law to govern parliamentary elections planned for June. The failure to agree on a law could delay the vote.

Also, the Hezbollah-dominated Cabinet has refused to extend the tenure of Maj. Gen. Ashraf Rifi, Lebanon's police chief, who is considered a foe by the Islamic militant group.

In his speech, Mikati said Rifi's departure would send the police department into "a vacuum."

Lebanese President Michel Suleiman must accept Mikati's resignation for it to be official, a step that is all but a formality.

This will open the way for a new round of political jockeying as the parliamentary blocs try to build coalitions to choose a new prime minister. Top posts will remain vacant until a new Cabinet is in place.

In Washington, State Department spokeswoman Victoria Nuland said the U.S. was "watching the situation in Lebanon very, very carefully."

"Our basic view of this is that we believe the Lebanese people deserve a government that reflects their aspirations and one that will strengthen Lebanon's stability, its sovereignty and its independence," she told reporters. "And we have grave concerns about the role that Hezbollah plays."

Mikati has been prime minister since June 2011, heading a government dominated by Hezbollah and its allies. Their main rivals are a Western-backed coalition headed by former Prime Minister Saad al-Hariri, son of Rafik Hariri, who was also Prime Minister and killed in a truck bombing in 2005.

A Harvard-educated billionaire, Mikati was chosen to lead the government after Hezbollah forced the collapse of Lebanon's previous, pro-Western government over fears a U.N.-backed tribunal investigating the killing of the elder Hariri would indict Hezbollah members.

But Mikati's relations with Hezbollah have never been smooth. He has rejected the notion that he serves Hezbollah or that his government will act as an Iranian proxy. Hezbollah accuses him of loyalty to the rival camp.

Mikati's resignation may be an attempt to boost his credentials among his fellow Sunni Muslims ahead of the upcoming election and amid the violence in Tripoli, his hometown.

____

Associated Press writer Bradley Klapper contributed reporting from Washington.

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    Political assassinations in Lebanon have occurred with impunity for decades. While Syria has been blamed for many of the killings, no one has been held accountable. In 2005, Syria was widely accused of involvement in the killing of former Prime Minister Rafik Hariri, a wealthy businessman and an influential Sunni politician. Hariri was hailed in Lebanon for rebuilding Beirut after the 15-year civil war. Following his death in a car bomb explosion, Damascus was forced to withdraw its troops and Syria's grip in Lebanon began to slip. <em>Caption: Lebanese Prime Minister Rafik Hariri addresses a news conference at his Paris residence Monday April 15, 1996. (AP PHOTO/Lionel Cironneau)</em>

  • Political Assassinations

    Many Lebanese residents accused Assad's regime of being behind Friday's assassination of Brig. Gen. Wissam al-Hassan, a Sunni, who headed the intelligence division of Lebanon's domestic security forces that has been probing the assassination plot against Hariri. Al-Hassan and his agents have been credited with identifying Samaha, the former information minister, as Syria's link to Lebanon. <em>Caption: Lebanese advertising workers erect a poster of Brig. Gen. Wissam al-Hassan with Arabic writing that reads, "the martyr of Lebanon's dignity," a day after a car bomb attack killed al-Hassan and at least seven others in downtown Beirut, Lebanon, Saturday, Oct. 20, 2012. (AP Photo/Hussein Malla)</em>

  • Hezbollah

    The Iran-backed Hezbollah has been Syria's most powerful ally in Lebanon, particularly since Damascus ended its military presence in Lebanon seven years ago. The Shiite militant group has dominated Lebanese politics for more than a decade and is now in control of the government. In 2006, Hezbollah gained support from Sunnis and Christians during a 34-day war with Israel, although Lebanon's southern villages and towns and the predominantly Shiite suburbs of Beirut sustained heavy damage. <em>Caption: In this Monday Sept. 17, 2012, photo, Hezbollah leader Sheik Hassan Nasrallah speaks to his supporters in a southern suburb of Beirut, Lebanon. (AP Photo/Hussein Malla)</em>

  • Hezbollah

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  • Hezbollah

    Since the beginning of the Syrian uprising, Hezbollah has sought to distance itself from the turmoil in Syria, although there have been allegations that the group has sent fighters to help Assad's regime fight rebels. Hezbollah's leader, Sheik Sheik Hassan Nasrallah, has not publicly sanctioned any operations in support of Assad, and warned the mayhem in the neighboring country was out of the group's control. <em>Caption: Lebanese Shiite movement Hezbollah and Amal supporters march with their party flags during a demonstration in the town of Hermel, in the northern Lebanese Bekaa valley, on September 23, 2012. (AFP/GettyImages)</em>

  • Troops On The Ground

    Lebanon's 15-year civil war ended in 1990 with Syrian forces defeating opponents, controlling large parts of the country and installing allied governments in Beirut. Syrian forces moved into Lebanon in 1976 as peacekeepers after the country got engulfed in civil war between Christian and Muslim militias. <em>Caption: Syrian soldiers take position 17 April 1990 in one of West Beirut districts as they have been deployed after heavy inter-Shi'ite clashes between pro-Syrian Amal movement and pro-Iranian Hezbollah militia. (RABIH MOGHRABI & RAMZI HAIDAR/AFP/Getty Images)</em>

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    Syrians were drawn into the conflict, and clashed with the Israeli troops after the 1982 invasion aimed at driving out Palestinian guerrillas. <em>Caption: Israeli children look at the nearby Syrian village of Jebata al-Khashabn as they sit on an old tank near the village of Buqaata at the Israeli side of the border on July 24, 2012 in the Golan Heights. (Photo by Uriel Sinai/Getty Images)</em>

  • Troops On The Ground

    In 2000, Bashar Assad became president of Syria, succeeding his late father, Hafez Assad. Israel withdrew from South Lebanon, increasing pressure on Syria to leave. Syrian troops pulled out five years later, after sweeping street protests following Hariri's assassination. Many in Lebanon and its Western-backers blamed Syria for the killing. Damascus has denied involvement. <em>Caption: In this picture taken on June 13, 2000, Syrian President Bashar al-Assad, right, his brother Maher, centre, and brother-in-law Major General Assef Shawkat, left, stand during the funeral of late president Hafez al-Assad in Damascus, Syria. (AP Photo, File)</em>