Western diplomats say the UN's top human rights body will hold an urgent meeting on Friday to discuss the situation in Syria.

It will be the third special session of the Geneva-based Human Rights Council since the start of the uprising against Syria's President Bashar Assad in March. Diplomats told The Associated Press on Tuesday that more than 20 of the council's 47 members have signed the call to hold the meeting.

They spoke on condition of anonymity as an official announcement wasn't due until later on Tuesday. An expert panel appointed by the council released a report Monday claiming that Syrian forces have committed "crimes against humanity" by killing and torturing hundreds of people, including children, in their efforts to quash the uprising.