Syrian government air strikes and artillery killed 71 people in the eastern Ghouta pocket near Damascus over the past 24 hours, the Syrian Observatory for Human Rights monitoring group said on Monday.
The Britain-based group said bombardment of the opposition-held enclave started escalating on Sunday evening, wounding 325 people. There was no immediate comment from the Syrian military.
Regime forces launched air and ground attacks on several districts in the suburb, which has been under a crippling siege since 2012.
Ten civilians, including children and women, were killed in Hammuriya town in Eastern Ghouta, the sources with the White Helmets civil defense agency said.
Four people were also killed in ground attacks in Saqba town, while three others were killed in an airstrike in Cisrin town, the sources added on condition of anonymity due to safety concerns.
Eastern Ghouta falls within a network of de-escalation zones -- endorsed by Turkey, Russia and Iran -- in which acts of aggression are expressly prohibited.
Nevertheless, the Syrian regime continues to target residential parts of the city, killing at least 539 people -- and injuring more than 2,000 others -- since Dec. 29 of last year.
Home to some 400,000 civilian residents, Eastern Ghouta has remained under a crippling regime siege for the last five years.
Syria has only just begun to emerge from a devastating conflict that began in 2011, when the regime cracked down on demonstrators with unexpected ferocity.