Syrian army bombardments killed 21 people in a Damascus suburb as a refugee agency said more than 200,000 people had now fled the country.

More than 3500 Syrians crossed into Turkey in the last 24 hours, Turkish officials said – one of the highest daily totals since the protests against President Bashar al-Assad started in March 2011.

"In Jordan, a record 2200 people crossed the border and were received at Zaatari camp in the north," Adrian Edwards, spokesman for the UN High Commissioner for Refugees said.

Assad's tough response to unrest inspired by Arab uprisings in Tunisia, Egypt and elsewhere has spawned an armed insurrection and plunged Syria into a civil war in which more than 18,000 people have died.

There was no let-up in the violence yesterday.

The Syrian army pounded the Damascus suburb of Daraya, where the 21 deaths reported by opposition activists brought the toll from the assault to 70.

Assad's forces are trying to regain control of the capital's outlying districts such as Daraya, a Sunni Muslim working class township that sprawls among farmlands where insurgents often take refuge after attacking troops.

Soldiers fired rocket launchers and artillery into Daraya where rebels were still holed up.

Fighting was also taking place in several middle class Sunni suburbs around Damascus, including Qatana, Sbeineh, Qadam, Assali and Hajar al-Aswad, opposition activists said.

Assad's elite forces, mostly drawn from his minority Alawite sect and increasingly used to keep control of Damascus, are based in hilltop compounds in the capital and surrounding areas.

At least 220 people were killed across Syria on Thursday, rebels said.