(Reuters) -

U.N.-appointed inspectors, blocked from entering Syria, are in Turkey to gather information about possible use of chemical weapons in the civil war, officials said on Thursday.

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 in which the death toll is estimated at more than 100,000.

The United States and its European allies have concluded that the Syrian government used chemical weapons, which Washington called a "red line" that justified providing military aid to the rebels.

Members of the team assembled by U.N. Secretary-General Ban Ki-moon had been on standby in Cyprus since April, unable to enter Syria as Western governments accused President Bashar al-Assad's forces of chemical weapons attacks.


The team went to Turkey this week and its head, Swedish scientist Ake Sellstrom, met Turkish Foreign Minister Ahmet Davutoglu on Thursday, a senior Turkish official told Reuters.

Sellstrom is expected to deliver an interim report in July, which U.N. diplomats said may just be oral and is expected to be inconclusive since it is impossible for him to make definite pronouncements about the chain of custody of the samples he has received from Britain, France and the United States.

One senior Western diplomat, speaking on condition of anonymity, said that Britain and the United States alone have notified U.N. Secretary-General Ban Ki-moon of 10 separate incidents of the use of chemical weapons by Assad's forces.

The diplomat also said Sellstrom would be visiting Berlin soon to discuss his investigation.

FRUSTRATED

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 U.N. mission has been unable to make progress on investigating the chemical weapons 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 interviews 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, the official said.

Syria is one of seven countries that has not joined the 1997 convention banning chemical weapons. Western countries believe it has stockpiles of undeclared mustard gas, sarin and VX nerve agents.

Assad's government says accusations by the United States, Britain and France that it used chemical weapons are an attempt to justify foreign military intervention.

(Additional reporting by Lou Charbonneau in New York; Editing by Peter Graff)

By Anthony Deutsch and Parisa Hafezi