Turkish Prime Minister Tayyip Erdogan has called for Syrian President Bashar al-Assad to step down for the sake of peace in the region and to stop any more bloodshed.

"Without spilling any more blood, without causing any more injustice, for the sake of peace for the people, the country and the region, finally step down," Mr Erdogan told a meeting of his ruling AK Party.

Meanwhile, Syrian forces reportedly killed 12 civilians in the central province of Homs today in an ongoing crackdown on the most defiant centre of opposition to President Assad.

Four boys aged ten to 15 were among those killed, according to the Syrian Observatory for Human Rights.

An Arab League deadline for Mr Assad to pull the military out of urban centres, free political prisoners and start a dialogue under the 22-member group's initiative to end the bloodshed in Syria expired at the weekend.

Mr Assad said in an interview published on Sunday he would not bow to international pressure to stop the crackdown on the protests against his rule.

The United Nations says 3,500 people have been killed in the crackdown.