Syrian army tanks and artillery shelled two Damascus suburbs on Wednesday after rebels allegedly attacked forces loyal to President Bashar al-Assad.

The military struck the suburbs of Harasta and Irbin hard, activists in the city reported. The towns were once held by opposition fighters but were retaken by the Syrian army two months ago, and are again under attack as retaliation for a raid against a government intelligence compound.

The Free Syrian Army mounted a series of operations after nightfall and the army is retaliating strongly, an activist named Raed told Reuters.

The Free Syrian Army (FSA) is a group of defected Syrian soldiers who have been fighting to take control of the country away from Assad, as well as protecting nonviolent activists and civilians in cities like Homs, which the government has been shelling for over a month. With only light arms and a shrinking ammunition supply, the FSA has been successfully pushed back by pro-Assad forces for the past few weeks.

Tanks entered residential neighborhoods, especially in southeastern areas of Deir al-Zor. The Free Syrian Army pulled out to avoid a civilian massacre, the Deir al-Zor Revolution Committees Union said in a statement.

The towns of Harasta and Irbin are home primarily to Sunni Muslims -- Sunnis are the religious majority in Syria but are becoming  resentful of the country's minority Shia Alawite government, suggesting the current conflict is starting take on religious and sectarian overtones.

A Sunni group claimed responsibility for bombings in the capital over the weekend. Al-Nusra Front to Protect the Levant said it led the suicide bombings that killed 27 people in Damascus to avenge the massacre of Sunnis.

The soldiers ... have carried out a series of military operations on the regime's lairs, most notably the air security and criminal security branches in Damascus, the group said in a statement.

We would like to inform the regime that our response to its crimes in Karm al-Zeitoun - the killing of families, children, women and the elderly, and the rape of women - is coming soon, God willing... Stop your massacres of Sunnis, or bear the sin of the Nusayris (Alawites). What is coming will be even more calamitous and bitter.

More than 8,000 people have been killed during the year-long uprising in Syria, according to the United Nations. The continued violence has been condemned by world powers, and on Tuesday Assad's tactics were criticized by one of his last remaining allies.

We believe the Syrian leadership reacted wrongly to the first appearance of peaceful protests and ... is making very many mistakes, Russian Foreign Minister Sergei Lavrov told the Kommersant-FM radio station.

This, unfortunately, has in many ways led the conflict to reach such a severe stage.