Syrian activists say several rocket-propelled grenades hit a ruling Baath Party building in Damascus Sunday, as President Bashar al-Assad vowed he will not “bow down” to international pressure to ease his brutal crackdown on dissent.

The Local Coordination Committees activist network and several residents Sunday reported numerous explosions in the center of the Syrian capital. They said fire trucks were headed to the area amid a heavy police presence. There was no immediate verification of the reports, and other eyewitnesses saw no signs of damage.

The Free Syrian Army, a group of dissident soldiers based in neighboring Turkey, claimed responsibility for the attack.

If confirmed, it would be the first significant assault on a government building in the Syrian capital since the anti-government uprising began in March. The reported incident occurred hours after an Arab League deadline passed for Damascus to end the bloodshed.

Meanwhile, in an interview published in Britain's Sunday Times newspaper, Mr. Assad said Syrians would vote in February or March for parliament to create a new constitution. But the embattled president vowed to continue his security crackdown against “militants” who he says are massacring Syrians on a daily basis.

He also repeated earlier warnings that any foreign military intervention in Syria would “shake the entire Middle East.”

On Saturday, activists said at least 15 people were killed across Syria, mostly in fresh raids by security forces. At least two army deserters died in clashes in Homs.

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

Last week, the 22-member Arab League suspended Syria's membership. A proposal by the league 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.

Meanwhile, Turkish Prime Minister Recep Tayyip Erdogan said Syria was responsible for the deteriorating relations between the two countries. He accused Syria of not fulfilling promises to Turkey, the Arab League and to the world for reform or to stop the bloodshed

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.

Meanwhile, British Foreign Secretary William Hague said he would meet with Syrian rebel leaders in London Monday. Hague has condemned the violence and called for Mr. Assad to step aside.