UNITED NATIONS - UN experts will travel to Syria as soon as possible to investigate three alleged incidents of chemical weapons attacks, the United Nations announced Wednesday.

UN spokesman Martin Nesirky said the green light for the investigation followed "the understanding reached with the government of Syria" during last week's visit to Damascus by UN disarmament chief Angela Kane and the head of the chemical weapons investigation team, Ake Sellstrom.

The announcement caps more than four months of behind-the-scenes talks aimed at getting chemical experts on the ground to investigate more than one alleged incident. Whether any signs of chemical weapons use remain at the three sites months after their alleged use remains to be seen.

The mandate of the investigation team is to report on whether chemical weapons were used, and if so which chemical weapon, but not to determine the responsibility for an attack.

When Secretary-General Ban Ki-moon agreed to a UN investigation in March, he said the announcement "should serve as an unequivocal reminder that the use of chemical weapons is a crime against humanity."

Nesirky said Sellstrom's team will visit Khan al-Assal, a village on the southwestern outskirts of the embattled city of Aleppo, which was captured by the rebels last week and was under attack by government forces Wednesday. The government and rebels blame each other for a purported chemical weapons attack on the village on March 19 that killed at least 30 people.

Nesirky did not give any details of the other two incidents to be investigated. A well-informed UN diplomat, speaking on condition of anonymity because discussions on the issue have been private, said Sellstrom is expected to choose the two other sites based on the technical and scientific information the UN has received from governments, doctors, alleged victims and others.

Syria asked the secretary-general to investigate the Khan al-Assal incident and balked at a broader investigation sought by Ban after Britain, France and the United States sent the UN information about other alleged attacks in Homs, Damascus, Aleppo and elsewhere.

UN Mideast envoy Robert Serry told the Security Council last week that the UN has received 13 reports of alleged chemical weapons use in Syria.

"The secretary-general remains mindful of other reported incidents," Nesirky said Wednesday, "and the mission will also continue to seek clarification from the member states concerned."

The diplomat stressed that the chemical weapons experts ought have access to all 13 sites in the future.  Last week, the Syrian National Coalition, the Western-backed opposition group, told members of the UN Security Council that it would provide access to a UN investigation team to any sites they control, the diplomat said.

Britain and France initially raised allegations of chemical weapons use in two locations in Khan al-Assal and the village of Ataybah in the vicinity of Damascus on March 19 and in Homs on December 23.

On June 13, the United States said it had conclusive evidence that Syrian President Bashar Assad's regime had used chemical weapons against opposition forces. That crossed what President Barack Obama had called a "red line" and prompted a U.S. decision to send arms and ammunition to the opposition, not just humanitarian aid and non-lethal material like armored vests and night goggles.  

In a letter to the secretary-general the following day, then-U.S. Ambassador Susan Rice said the United States had determined that the nerve agent sarin was used in the March 19 attack on Khan al-Assal and also in an April 13 attack on the Aleppo neighborhood of Shaykh Maqsud. She said unspecified chemicals, possibly including chemical warfare agents, were used May 14 in an attack on Qasr Abu Samrah and in a May 23 attack on Adra.

Russia's UN Ambassador Vitaly Churkin said earlier this month that experts from Russia, Syria's closest ally, determined that Syrian rebels made sarin and used it in the March 19 attack on Khan al-Assal. The U.S., Britain and France reiterated at the time that they have seen no evidence to indicate that the opposition has acquired or used chemical weapons.

Churkin told reporters after delivering an 80-page report to the secretary-general that Syria asked Russia to investigate the attack after the UN team of chemical weapons experts was unable to enter the country because of the dispute over the probe's scope.

Churkin later gave copies of the report to the British, French and Americans who discovered that several pages were missing.

The Russian Foreign Ministry's deputy information director, Maria Zakharova, told AP that "there are in fact several pages missing which contain scientific technical information not having direct relation to the results of the analysis conducted by our experts that were presented to the UN Secretariat."

"These pages were intended for 'internal use' and did not influence the conclusion of the report in any way," Zakharova said. "The conclusion, as we have already stated, is that the munition filled with chemical warfare agents was produced and used on March 19 in the vicinity of Aleppo by non-governmental forces."