Syrian activists say several rocket-propelled grenades hit a ruling Baath Party building in Damascus Sunday, not long before the Arab League rejected amendments from President Bashar al-Assad's government to a plan that would end Syria's deepening crisis.

The Local Coordination Committees activist network and several residents reported numerous explosions in the center of the Syrian capital. They said fire trucks 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.

The League on Sunday rejected a request to amend plans that would send a 500-member monitoring mission to Syria to assess the situation there. The Cairo-based organization told Mr. Assad's government its proposals were not acceptable because they would introduce “drastic changes” to the observers' mandate.

Egypt's state news agency, MENA, reported Sunday that the 22-member Arab League will meet again Thursday to discuss the Syrian crisis. It suspended Syria's membership earlier this month.

In an interview published in Britain's Sunday Times newspaper, Mr. Assad vowed he will not “bow down” to international pressure to ease his brutal crackdown against “militants” who he says are massacring Syrians on a daily basis.

The embattled president said citizens will vote in February or March for parliament to create a new constitution. He also repeated earlier warnings that any foreign military intervention in Syria would “shake the entire Middle East.”

Turkish Prime Minister Recep Tayyip Erdogan said Syria is 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.

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