At least 32 civilians, including five children, were killed Thursday in Syrian regime air strikes and artillery bombardment on rebel-held areas in eastern Aleppo, the Syrian Observatory for Human Rights said, cited by AFP.

"There was an escalation in the evening, with successive bombardments," Observatory head Rami Abdel Rahman told AFP, adding that many people were trapped under rubble.

It was one of the heaviest since the regime launched an offensive on eastern Aleppo on November 15.

More than 250,000 civilians remain under siege in Aleppo as the Syrian army advances, AFP reports.