President Bashar al-Assad

REUTERS

Syrian forces clashed with rebels around Aleppo's television and radio station on Saturday, activists said, and a local rebel commander said his fighters were preparing for a "strong offensive" by government forces on the country's largest city.

Syrian troops back by armor stormed the last opposition bastion in Damascus on Friday in a drive to crush a rebel offensive that coincided with a bomb attack that killed four of President Bashar al-Assad's top security officials, reports Reuters.

Syria's civil war has intensified in the last few weeks, with fighting engulfing Damascus and Aleppo for the first time in the 17-month-old uprising against Assad family rule.

The two cities are crucial prizes for both sides in an increasingly brutal struggle that has eluded all attempts at a diplomatic solution and risks igniting a wider conflagration.

Former U.N. Secretary General Kofi Annan, who is quitting as international peace envoy for Syria, said in a commentary on Thursday Assad should step down, urging Syria allies Russia, China and Iran to persuade him to embrace political transition.

Western and Arab powers want Assad to step aside but Russia and China have used their Security Council vetoes to block attempts to force him out. They say outside interference is prolonging the bloodshed.

U.N. member states on Friday voted overwhelmingly to condemn the Syrian government at a special session of the 193-nation General Assembly that Western diplomats said highlighted the isolation of Assad supporters Russia and China.

In Aleppo, a Syrian activist told Reuters the rebels had sought to extend their area of control from the Salaheddine district, where the most intense fighting has been focused, northwards to the area around the television and radio station.

"The Free Syria Army pushed from Salaheddine to al-Adhamiya where they clashed this morning with Syrian troops. But they had to retreat," activist Barraa al-Halabi told Reuters.

A 19-year-old fighter called Mu'awiya al-Halabi, who was at the scene said Syrian snipers surrounded the station and targeted the rebels.

"We were inside it for a few hours after clashes with the Syrian army but the Syrian army sent snipers and surrounded the TV station and as soon as morning came, the army started shooting. One of our fighters was martyred and four were wounded," he said.