BEIRUT — Syrian rebels say pro-government forces are pressing their assault on the eastern, rebel-held neighborhoods of Aleppo, this time attacking the city from the south in a bid to penetrate opposition-controlled areas.

The Islamic Front rebel coalition said on Twitter on Tuesday that its factions repelled an advance on the Sheikh Saeed neighborhood.

The Britain-based Syrian Observatory for Human Rights says the government offensive is accompanied by airstrikes on the contested neighborhoods.

The monitoring group says more than 400 civilians have been killed in and around Aleppo since the collapse of a U.S. and Russian-brokered cease-fire two weeks ago, mainly in the rebel-held east of the embattled city.

In the offensive, health facilities and hospitals have repeatedly come under attack.