From the centre of Damascus, Syrians can see the shrouds of smoke rising overhead and feel the shake of explosions that warn of a frontline creeping ever closer.

Damascus is bracing itself after nearly two years of civil conflict as rebel forces seep deeper into the capital, and anxiety is etched across the faces of people in the city centre.

"There is fear and pain in people's hearts, a feeling of despair and paralysis because of the enormity of the crisis," said Suad, an architect in the Salihiya neighborhood. "The sounds of all the different explosions - mortar, artillery and warplanes - suggest the frontline is getting closer," she said.

This ancient city has survived conquests down the ages, from Alexander the Great to early Arab caliphs and Crusaders. Sacked by Mongol invaders in 1400, it was later taken by the Turks and seized more than once by European armies last century. Now Damascus is under attack again, this time by its own people.

On Sunday, warplanes raided the Palestinian refugee district of Yarmouk, one of the most densely populated parts of the capital, where concrete homes are piled upon each other. The air strike, believed to have killed 25 people, was the closest yet to the city centre, little more than a mile away.

The army has warned Yarmouk's impoverished Syrian and Palestinian residents to flee in preparation for a "cleansing" operation, as bombardment ratchets up the intensity of a week of internal clashes between Palestinians for and against Assad.

A new wave, thousands-strong is now seeking refuge. They are the latest victims of violence that has already forced people to flee many suburbs around Damascus, as rebels tighten their grip on the eastern outskirts of the city and its southern districts.

Um Hassan's family is fleeing for the third time in months. They fled two sieges of other rebel-held suburbs. Now their new rented apartment in Yarmouk is under fire: "Once again, I have to move. I really don't know when this will end," she said.

"God help us."