The military chief of the main umbrella group of Syrian rebels, the Free Syrian Army, has accused Hezbollah fighters of "invading" Syria, BBC News reported.

Gen Selim Idriss claimed that more than 7,000 fighters of the Lebanese Shia movement were taking part in attacks on the rebel-held town of Qusair.

The French foreign minister has estimated the number at 3,000-4,000.

The U.S. State Department has demanded that Hezbollah withdraw its fighters from Syria immediately.

A spokeswoman Jen Psaki said their presence was an "extremely dangerous" escalation.

The statements follow a meeting of the UN Human Rights Council in Geneva, which condemned government attacks on Qusair and the involvement of foreign fighters.