AMMAN, Jordan -- Syrian government jets bombarded the Damascus ring road yesterday in a bid to halt a rebel advance that threatens President Bashar Assad's hold on the capital, insurgent commanders and opposition activists said.

Warplanes fired rockets at southern parts of the route where rebels have spent the past 36 hours overrunning army positions and road blocks encircling the heart of the city, the site of key state security and intelligence installations.

Assad, battling to crush a 22-month-old revolt in which 60,000 people have died, has lost control of large parts of the country but his forces, backed by air power, have so far kept rebels away from the center of Damascus.

World powers fear the conflict -- the longest and deadliest of the uprisings that started spreading through the Arab world two years ago -- could envelop Syria's neighbors, further destabilizing an already explosive region.

"The regime really wants its positions on the ring road back. It is a major defense line for the capital," said Aby Ghazi, a rebel commander based in the eastern suburb of Irbreen.

Ghazi said the rebels have reached the edges of the city's main Abbaside Square where the Syrian military had turned a football stadium into barracks.

Units of Assad's elite Republican Guard based on the imposing Qasioun Mountain overlooking the capital fired artillery rounds and rockets at Jobar, an eastern neighborhood bordering the square, and at the ring road, rebel and activist sources said.

In Cairo, leaders of Muslim nations called on Thursday for a "serious dialogue" between Syria's government and an opposition coalition on a political transition to end the civil war, but pinned most of the blame for the bloodshed on the state.

A two-day summit of the 57-member Organization of Islamic Cooperation backed an initiative by Egypt, Turkey, Iran and Saudi Arabia to broker negotiations to stop the fighting. The final communique said Assad's government was most to blame.

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