Witnesses and opposition activists in the Syrian capital of Damascus are reporting heavy fighting between rebels and government forces.

The witnesses tell international news agencies that they could hear machine gun fire and rocket-propelled grenades exploding in al-Mezze — one of the most heavily guarded neighborhoods of Damascus and home to government security facilities.

There is no word so far on casualties.

Sunday a car bomb blew up near a government security building in the northern city of Aleppo, killing two people and wounding 30.

The state-run news agency blames terrorists while the opposition says the government is responsible.

Also Sunday, Syrian security forces broke up a rally in Damascus marking one year since the start of anti-government protests. Hundreds of people tried to march. Police arrested several prominent opposition leaders.

Government forces also prevented anniversary marches in other cities.

Two blasts minutes apart in killed 27 people and wounded more than 100 on Saturday in Damascus. No one has claimed responsibility for either attack. Aleppo and Damascus are both seen as having high levels of support for President Bashar al-Assad.

Former U.N. chief Kofi Annan, who met Mr. Assad in Damascus last week, has ordered a team of experts to Syria Monday to discuss a possible cease-fire and international monitoring mission.

The United Nations says at least 8,000 people have been killed in the Assad government's violent crackdown on the revolt, which began with peaceful protests and became increasingly militarized as army defectors attacked pro-Assad troops who assaulted civilians.