At least 13 people have been killed in unrest across Syria, where the government is facing a midnight deadline from the Arab League to end its crackdown on dissent.

Activists say most of Saturday's deaths took place as Syrian troops launched new raids in several regions. They say at least two army deserters died in clashes with security forces in the Homs region.

The state-run SANA news agency says authorities raided the “hideouts of terrorists groups” on Saturday and arrested more than 140 “wanted men.”

The Arab League has set a deadline of midnight, local time, for Syria to end the crackdown on risk sanctions. The 22-member bloc has already suspended Syria's membership.

The league's plan also calls for Damascus to allow in teams of observers to monitor its compliance. On Friday, Syria agreed to the plan “in principle,” but had submitted unspecified amendments that were under review.

Damascus has been facing mounting international pressure to end the unrest that the U.N. says has resulted in more than more than 3,500 deaths.

On Friday, U.S. Secretary of State Hillary Clinton expressed concern that Syria could slide into civil war.

Meanwhile, British Foreign Secretary William Hague will meet with Syrian rebel leaders in London Monday. Hague has condemned the violence and called for Syrian President Bashar al-Assad to step aside.