DAMASCUS, Syria — After months of drawn-out negotiations, United Nations experts arrived in Damascus on Sunday to begin their investigation into the purported use of chemical weapons in Syria's civil war.

The rebels, along with the U.S. and other Western powers, have accused President Bashar Assad's regime of carrying out the alleged chemical attacks, while the Syrian government and Russia have blamed the opposition. Nearly six months after the weapons of mass destruction were first allegedly employed on the battlefield, definitive proof remains elusive.

The U.N. team that arrived in Damascus on Sunday is tasked with determining whether chemical weapons have been used in the conflict, and if so which ones. But the mission's mandate does not extend to establishing who was responsible for an attack, which has led some observers to question the overall value of the probe.

The 20-member U.N. delegation, led by Swedish chemical weapons expert Ake Sellstrom, checked into a five-star hotel upon arrival in central Damascus. Plainclothes police officers immediately whisked them away from a crush of reporters and cameraman waiting in the lobby.

U.N. spokesman Martin Nesirky said the team will begin its work on Monday.

The investigators are expected to visit three sites where chemical weapons attacks allegedly occurred: the village of Khan al-Assal just west of the embattled northern city of Aleppo and two other locations that have not been disclosed.

Syria is said to have one of the world's largest stockpiles of chemical weapons, including mustard gas and the nerve agent sarin. There are concerns that the Assad regime might use them on a large scale, transfer some of them to the Lebanese militant Hezbollah group or that the chemical agents could fall into the hands of al-Qaida-affiliated militants and other extremists among the rebels.

Ahead of the experts' arrival, Syrian Deputy Foreign Minister Faisal Mekdad told The Associated Press that the government will offer the U.N. inspectors its full assistance.

"I assure you, on behalf of the Syrian Arab Republic, that we will fully cooperate with this team and provide it will all information we have and all facilities to reach a rational conclusion," he said.

"Our basic target is for this team to find facts on ground, especially about what happened in Khan al-Assal, because we, as a government, do not know about any other cases other than the case where chemical weapons were used by terrorists there," he added. Syria's government refers to rebels fighting its rule as terrorists.

A spokesman for the Western-backed Syrian opposition's military wing, Loay al-Mikdad, also welcomed the U.N. mission, but was skeptical about how fruitful the investigation will be.

"We hope that this delegation will be able to reach all areas where unconventional weapons have been used," al-Mikdad said. "However, we're absolutely sure that this regime that has done everything from changing signs with the names of areas to fabricating evidence with past delegations will do the same with this one. Therefore, we doubt they will be able to uncover truthful results."

Al-Mikdad said the rebels, if asked, will facilitate a visit by inspectors to opposition-held areas, and that no restrictions would be placed on their movements.

The Syrian government initially asked the U.N. to investigate an alleged chemical weapons attack on March 19 in Khan al Assal, which was captured by the rebels last month. The government and rebels blame each other for the purported attack which killed at least 30 people.

Britain, France and the U.S. followed with allegations of chemical weapons use in Homs, Damascus and elsewhere. U.N. Mideast envoy Robert Serry told the Security Council last month that the U.N. has received 13 reports of alleged chemical weapons use in Syria.

Speaking to the AP, Mekdad insisted that Syria "will never use chemical weapons against its people."

"We said that these weapons were used in Syria, and Syria was the first to inform the United Nations that armed groups used these weapons in Khan al-Assal," the Syrian deputy foreign minister said. "We had wished that the United Nations had conducted the investigation immediately at the time so the team would not find difficulties gathering evidence."

In June, the U.S. said it had conclusive evidence that Assad's regime used chemical weapons against opposition forces. That crossed what President Barack Obama called a "red line," prompting a U.S. decision to begin arming rebel groups, although that has not happened yet.

The alleged chemical attacks are just one facet of the bloody conflict in Syria that has killed more than 100,000 people and spilled over into neighboring countries.

On Sunday, three rockets fired from Syria landed on the Lebanese border town of Hermel, causing damage but no casualties, security officials said. They spoke on condition of anonymity because they weren't authorized to brief the media.

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Associated Press writer Jamal Halaby in Amman, Jordan, and Ryan Lucas and Yasmine Saker in Beirut contributed to this report.

Earlier on HuffPost:

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  • A Syrian rebel tries on a gas mask seized from a Syrian army factory in the northwestern province of Idlib on July 18, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Syrian volunteers try to evacuate 8-year-old Mahmud Fayad still trapped under the rubble of a destroyed house after a barrel bomb was dropped from an air force helicopter in Saraqeb in northwestern Syria on July 20, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • In this photo released by the Syrian official news agency SANA, Syrian citizens gather near damaged cars that were burned after a car bomb exploded in the suburb of Jaramana, Damascus, Syria, Thursday, July 25, 2013. (AP Photo/SANA)

  • An Indian Shiite Muslim woman breaks down as she holds a placard during a protest rally organized to condemn an attack on a Shiite shrine in Syria, in Bangalore, India, Friday, July 26, 2013. (AP Photo/Aijaz Rahi)

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  • In this photo released by the Syrian official news agency SANA, Syrian citizens gather near damaged cars that were burned after a car bomb exploded in the suburb of Jaramana, Damascus, Syria, Thursday, July 25, 2013. (AP Photo/SANA)

  • Syrians inspect the site where a barrel bomb dropped by an air force helicopter exploded in Saraqeb in northwestern Syria on July 20, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

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  • In this photo released by the Syrian official news agency SANA, Syrian citizens look at a damaged building after a car bomb exploded in the suburb of Jaramana, Damascus, Syria, Thursday, July 25, 2013. (AP Photo/SANA)

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  • In this Wednesday, July 3, 2013 citizen journalism image provided by Lens Young Homsi, which has been authenticated based on its contents and other AP reporting, shows Syrians inspecting the rubble of damaged buildings due to government airstrike and shelling, in the al-Hamidiyyeh neighborhood of Homs province, Syria. (AP Photo/Lens Young Homsi)

  • A picture taken on July 18, 2013 shows smoke rising from a building after opposition forces attacked a government forces held checkpoint in Syria's northeastern city of Deir Ezzor on July 18, 2013. (ABO SHUJA/AFP/Getty Images)

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  • A rebel fighter aims his weapon to Syrian government forces' positions inside a destroyed school in the Izaa district of Aleppo, on July 14, 2013. (JM LOPEZ/AFP/Getty Images)

  • A rebel fighter from the Suqur Al-Sham brigades, takes a nap after his night shift in a trench along the highway that connects Idlib city with Latakia, 100m far from the Syrian regime's forces's positions, on July 14, 2013. (DANIEL LEAL OLIVAS/AFP/Getty Images)

  • In this citizen journalism image provided by Aleppo Media Center AMC, which has been authenticated based on its contents and other AP reporting, buildings are seen damaged by Syrian government airstrikes and shelling in Aleppo, Syria, Monday, July 8, 2013. (AP Photo/Aleppo Media Center AMC)

  • Family members pray over the bodies of two Syrian children, Safia Baour, 14, and her three-year-old brother Khaled, who were killed after a shell landed on their family home as they gathered to break their fast with the iftar meal on July 13, 2013 in Maaret Al-Numan in southern Idlib province. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Syrian rebels head to the town of Bsankol in the northwestern province of Idlib to join comrades fighting regime forces for the control of the highway that connects Idlib with Latakia on July 11, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • An opposition fighter stands over seven year old Ahmad Jabir, who was injured alongside some his family members by a shell, as he lies on a X-Ray machine after he brought the boy to a hospital in the town of Al-Bara, in Syria's northwestern province Idlib on July 10, 2013. (DANIEL LEAL-OLIVAS/AFP/Getty Images)

  • Syrian rebels gather outside a building which they blew up to target a regime sniper taking shelter inside but who managed to escape in the Salaheddine district of the northern city of Aleppo on July 10, 2013. (SALAH AL-ASHKAR/AFP/Getty Images)

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  • This Tuesday, July 9, 2013 citizen journalism image provided by Aleppo Media Center AMC, which has been authenticated based on its contents and other AP reporting, shows Syrian rebels running during heavy clashes with Syrian soldiers loyal to Syrian President Bashar Assad, in the Salah al-Din neighborhood of Aleppo, Syria. (AP Photo/Aleppo Media Center AMC)

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