BEIRUT (AP) — Syrian government troops pushed into two northern Damascus neighborhoods on Friday, triggering heavy fighting with rebels as they tried to advance under air and artillery support, activists said.

The drive was the latest in a days-long offensive by government forces in and around the capital, an apparent bid to secure President Bashar Assad’s main stronghold against rebel challenges.

The Britain-based Syrian Observatory for Human Rights said the fighting between rebels and soldiers backed by pro-government militiamen was concentrated in the Jobar and Barzeh areas. The Local Coordination Committees, another activist group, said troops also bombarded the nearby neighborhood of Qaboun with mortars and multiple rocket launchers.

State-run news agency SANA said troops killed five rebels in clashes near the main mosque in Jobar. It added that many other “terrorists,” the term the government uses for rebels, were killed in the area and the nearby neighborhood of Zamalka.

The regime has largely kept the rebels at bay in Damascus, although opposition fighters control several suburbs of the capital from which they have threatened the heart of the city. Last month, government troops launched a campaign to repel the opposition’s advances near the capital, deploying elite army units to the rebellious suburbs and pounding rebel positions with airstrikes.

The Observatory also reported clashes in the northern city of Aleppo, Syria’s largest, between rebels and Kurdish gunmen in the contested Sheikh Maqsoud neighborhood. It also said there was fighting around the sprawling Abu Zuhour air base in the northwestern Idlib province.

Syria’s conflict started with largely peaceful protests against Assad’s regime in March 2011 but later degenerated into a civil war. More than 70,000 people have been killed, according to the United Nations.

On Thursday, the White House and other top Obama administration officials said that US intelligence has concluded with “varying degrees of confidence” that the Syrian government has twice used chemical weapons in the civil war, which has dragged on for two years.

However, officials also said more definitive proof was needed and the US was not ready to escalate its involvement in Syria beyond non-lethal aid despite President Barack Obama’s repeated public assertions that Syria’s use of chemical weapons, or the transfer of its stockpiles to a terrorist group, would cross a “red line.”

There was no immediate comment from Syrian authorities on the US statement.

Copyright 2013 The Associated Press.