Activists say Syrian security forces killed at least 16 people Friday as they launched new raids in some regions and shot at anti-government protesters.

They say the majority of deaths occurred in the southern Daraa region.

Protesters who rallied across Syria urged other countries to expel their Syrian ambassadors. Their calls follow a recent Arab League vote to suspend Syria's membership.

The league also gave Syria an ultimatum to end the bloodshed and allow in teams of observers to monitor compliance. On Friday, the group said Syria agreed to the plan “in principle,” but had submitted unspecified amendments that were now being studied.

Syria's state-run SANA news agency says thousands of demonstrators rallied in Damascus Friday to express their “rejection” of the league's decision.

British Foreign Secretary William Hague will meet with Syrian rebel leaders in London Monday. Hague, who has condemned the violence, has called for Syria's President Bashar al-Assad to step aside over the Syrian government's failure to end a crackdown on protesters.

Senior rebel leaders will also meet with officials from British Prime Minister David Cameron's office.

Meanwhile, French Foreign Minister Alain Juppe called for stronger sanctions and a United Nations Security Council resolution condemning Damascus. He told the French news agency “it is now too late” for Mr. Assad's government to change.

Juppe spoke after meeting in Istanbul with Turkish Foreign Minister Ahmet Davutoglu, who warned Syria could descend into civil war as fighting between Syrian army defectors and government forces intensifies.

The U.N. says at least 3,500 people have been killed in connection with the Syrian revolt since March. Syria has blamed much of the violence on foreign-backed terrorists and religious extremists.