Syrian regime air strikes killed at least five civilians in a rebel-held neighbourhood of Aleppo city, the Syrian Observatory for Human Rights said calling it a "serious violation".

The raids follow a lull in strikes brought by an unprecedented ceasefire that has largely held since coming into force on February 27.

"At least five civilians were killed in Syrian air force raids on the Salhin neighbourhood," according to Observatory director Rami Abdel Rahman.

"Friday's toll is the highest in Aleppo city since the ceasefire came into force and it is the most serious violation in the city since the truce came into effect," Abdel Rahman said.

He said 10 people were also wounded in the air strikes but warned that the toll could still rise as there were people trapped under the rubble.

An AFP correspondent in the city said the raids struck a mosque in Salhin.

On Thursday, a child was killed in regime bombardment of the rebel-held neighbourhood of Myassar, also in Aleppo city, said the Britain-based Observatory which monitors the Syria conflict.

More than 270,000 people have been killed since Syria's conflict first broke out in March 2011.