DAMASCUS United Nations chemical weapons experts will arrive in the Syrian capital on Monday to begin a two-week investigation into alleged chemical strikes at three locations in the war-torn country, a long-awaited breakthrough that ends months of negotiations between the U.N. and Syria's government.
An alleged chemical attack in the village of Khan al-Assal, near the northern city of Aleppo, in March sparked a blame game between the Syrian government and opposition groups.
The U.N. gave a green light for the investigation last week following an "understanding" reached between the Syrian government, U.N. disarmament chief Angela Kane and Swedish professor Ake Sellstrom, who will lead the team of investigators, according to U.N. sources.
The sources tell CBS News that Sellstrom, a former U.N. weapons inspector in Iraq, will lead a team of about 10 experts from the Organization for the Prohibition of Chemical Weapons (OPCW) and the World Health Organization.
"The team would arrive in Beirut on Sunday and would hit the road to Damascus early Monday and start immediate talks with the Syrians," said one U.N. official. He spoke on the condition of anonymity because the precise plans had not been made public. "They will stay in the country for some two weeks," he added.
The U.N. inspection team has been ready to go into Syria since April to try and verify claims that a chemical agent -- reportedly Sarin gas -- was used in the Khan Assal attack, but reaching the agreement with the Syrian government over logistics on the ground has delayed their arrival since then.
Syria is one of seven countries that has not joined the 1997 convention banning chemical weapons. The U.S. and its allies believe Syria has stockpiles of undeclared mustard gas, Sarin and VX nerve agents, and President Obama declared before the alleged attack in Khan Assal that any use of the deadly weapons would represent a "red line" for his administration and could draw direct U.S. involvement in the conflict.
The U.N. team is to carry out investigations in Khan Assal and two other locations, which were being kept secret for security reasons. Khan Assal recently fell back into rebel hands, and the U.S.-backed opposition coalitionit would welcome the inspectors to the village.
The team of inspectors, interpreters and medics faces a big challenge given the restrictions on travel within the country it agreed to in order to be granted access to Syria. Also hampering their progress will be the relatively small amounts of nerve agent likely used in the attacks, and the time that has passed since those attacks.
President Bashar Assad's government contends rebels were responsible for the purported March 19 Sarin gas attack in Khan Assal, which left 26 people dead. Assad initially invited the U.N. to inspect the site, but offered access only to that location.
The other, unconfirmed sites on the inspectors' list are likely Ataybah, a location near Damascus where a March attack has been alleged, and Homs, the focus of a possible December strike.
The United States, Europe and Russia largely agree that chemical weapons have been used in the conflict, butin blaming the opposition.
Western nations, on the other hand, say all the evidence points to Assad's forces using the weapons in "limited" quantities.
To try and build up a picture of the events at any particular site, inspectors will interview victims, witnesses, doctors and residents, some a fair distance from the scene, the U.N. sources said.
In a Sarin attack, about 85 percent of the chemical agent misses its target; it ends up in the soil, or blowing into other areas.
In addition to the personal interviews, inspectors will also conduct direct tests on soil and medical samples taken during their visits.
Sarin is volatile and breaks down quickly in contact with moisture. The process is speeded up by UV rays in sunlight, rain, humidity and wind. But traces of Sarin and other agents can still be found years after an attack.
The OPCW has portable equipment for running tests in the field, but Sellstrom's team will collect samples and send them to laboratories that make up the OPCW's global network.
The organization has labs in Great Britain, China, Russia, Japan and the U.S.
The announcement of the investigation capped more than four months of behind the scenes talks aimed at getting chemical experts on the ground, with Syria trying to limit the probe just to Khan Assal and the U.S., Britain and France pressing for a broader investigation.
The mandate of the investigation team is to report on whether chemical weapons were used, and if so which chemical agents, but not to determine the responsibility for any attacks.
Both the Syrian government and the opposition forces deny the use of chemical weapons. The United Nations last week said it had received 13 claims of chemical strikes, with corroborating material provided by Damascus, Moscow and three Western governments.
In June the Obama administration said it was to, citing alleged evidence that the regime had used small quantities of sarin gas in strikes.
Syria has been embroiled in war for nearly two and a half years, leaving more thanand millions more displaced internally and scattered to neighboring nations as refugees, according to the United Nations.