BEIRUT -- New airstrikes and shelling of the besieged, rebel-held suburbs of the Syrian capital killed at least 10 people and wounded dozens more on Wednesday, a rescue organization and a monitoring group said, adding to a staggering casualty toll that has overwhelmed paramedics and doctors in the past few days.

Syrian government forces and Russian aircraft have shown no signs of letting up their indiscriminate aerial and artillery assault on eastern Ghouta since they stepped up strikes late Sunday.

At least 260 people have been killed since Sunday night, according to the Britain-based Syrian Observatory for Human Rights monitoring group, including 10 in a wave of strikes on the town of Kafr Batna on Wednesday.

The Syrian Civil Defence search-and-rescue group, also known as the White Helmets, said government forces targeted the town with airstrikes, artillery fire, and barrel bombs -- crude, explosives-filled oil drums dropped from helicopters at high altitudes. It reported that several other people were wounded.

The locally-run Ghouta Media Center reported strikes on Kafr Batna and other towns in the region outside Damascus.

"We are really alarmed by the information we're receiving from civilian areas and the very high number of casualties. You cannot continue business as usual," said Panos Moumtzis, the U.N. regional humanitarian co-ordinator for the Syria.

"Ghouta is a 10-mile drive from the hospitals in Damascus and its heartbreaking to think of children, women, and elderly who are in need, unable to be evacuated, and in a situation of fear, hiding in basements and not being able to go out," he told The Associated Press by phone from Amman, Jordan.

The Russian military is supporting Syrian President Bashar Assad's forces and was instrumental to the all-out assault on the eastern half of Syria's largest city, Aleppo, in late 2016 to eject rebels from their enclave there.

Tens of thousands of civilians ended up fleeing their homes. Many have been unable to return. Hundreds more were killed in indiscriminate shelling and bombardment. A subsequent U.N. investigation charged that the campaign amounted to forced displacement of a population and rose to the level of a war crime.

Russian Foreign Minister Sergey Lavrov said earlier this week eastern Aleppo could serve as a model for eastern Ghouta.

Pro-government forces have been amassing since the weekend on the perimeter of the rebel-held region, a collection of towns and farmland that once provided grain and fruit to Damascus, before nearly seven years of warfare turned it into a landscape of havoc and despair.

At least 400,000 people have been killed in Syria's civil war, sparked by a violent crackdown on popular demonstrations against Assad in 2011.