Members of the team assembled by UN Secretary-General Ban Ki-moon had been on standby in Cyprus since April, unable to enter Syria as Western governments accused President Bashar Assad's forces of chemical weapons attacks.
They were sent to Turkey this week and its head, Swedish scientist Ake Sellstrom, was meeting Turkish Foreign Minister Ahmet Davutoglu on Thursday, a senior Turkish official told Reuters.
The Syrian government and rebels fighting it have accused each other of using lethal chemical agents, including sarin gas, in the two-year-old conflict.
More than 100,000 people have been killed since fighting began in March 2011 in what is the longest and most violent of the recent Arab uprisings, according to the British-based Syrian Observatory for Human Rights.
Western governments have grown frustrated that the UN mission has been unable to make progress on investigating the claims, a diplomat told Reuters.
From Turkey, the team will be unable to gather soil samples or scientific evidence needed to prove chemical use, but could compile intelligence and interview or take blood samples from witnesses or victims of alleged attacks.
"As he cannot travel to Syria, Sellstrom visits countries like Turkey, France and Britain that have some information about possible use of chemical weapons in Syria," said the Turkish official, who spoke on condition of anonymity.
Sellstrom visited the Turkey-Syria border area and talked to officials who shared data on chemical weapons use, he said.
Syria is one of seven countries that has not joined the 1997 Chemical Weapons Convention but is believed to have significant stockpiles of undeclared chemical weapons, including mustard, sarin and VX nerve agents.
Assad's government has rejected as lies assertions by the United States, Britain and France that its forces have used chemical weapons several times against Syrian citizens. It said the claims were an attempt to justify foreign military intervention.
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