The United States and Britain have provided United Nations experts with details of 10 suspected chemical weapons attacks by Syrian government forces, a UN diplomat said Wednesday.

The new revelations come as Western nations struggle to find ways to press for access to Syria for the UN team that has been waiting more than three months for Damascus to let it in.

Britain, France and the United States have each sent evidence of alleged attacks to the UN for the team led by Swedish expert Ake Sellstrom.

The incidents started in December and run through to May, according to diplomats.

The British and Americans have between them notified the UN of 10 separate incidents, said one UN diplomat.

"There is some overlap between the American ones and the British ones, if you add them all up there are 10 separate incidents where there seems to have been use of chemical weapons by the regime," the diplomat said on condition of anonymity.

Few details have emerged of France's evidence to the UN panel. But all of the Western countries say they have no evidence that opposition rebels have used chemical arms.

President Bashar al-Assad's government originally asked for a UN investigation after accusing rebels of using chemical arms in the 27-month-old conflict that according to activists has left 100,000 dead.

But it has refused to give access to Sellstrom and his experts after UN leader Ban Ki-moon insisted that all alleged attacks be probed.

Ban has repeatedly demanded "unfettered access." But the United Nations has also said that the details submitted by the Western countries cannot be considered as proof since experts must gather their own firsthand evidence from the scene.

Sellstrom was in Turkey this week as part of his mission. Diplomats said he was to speak with doctors who had treated victims of the attacks.