Hundreds of youths from nearby villages were shot at when they tried to march into the centre of the southern city.

A Syrian human rights activist said that at least 37 had died.

Troops also reportedly shot at people attending the funerals of six people killed in a raid on a mosque overnight.

Before the violence on Wednesday afternoon, at least 12 people had been killed in clashes with the security forces in the southern city.

UN Secretary General Ban Ki-moon has called for a "transparent investigation" and for those responsible to be held accountable.

The US state department has said it is "deeply concerned by the Syrian government's use of violence, intimidation and arbitrary arrests to hinder the ability of its people to freely exercise their universal rights".