The heaviest shelling in recent weeks has shaken the main city in Ukraine's rebel-held east, heightening worry about the renewal of full-scale conflict despite a cease-fire signed two months ago between Ukraine and Russia-backed separatists.

Artillery explosions roared throughout the early hours of Sunday in Donetsk, quietening only after sunrise. A city council statement said four residential buildings were destroyed, but it didn't give information on casualties.

The cease-fire called on Sept. 5 has been violated almost daily. Some of the heaviest fighting focuses on Donetsk's airport.

On Saturday, Associated Press reporters saw scores of military vehicles moving near Donetsk and farther to the east. Many of the unmarked vehicles were towing artillery. Ukrainian officials say rebel forces have received new weaponry and manpower from Russia. Moscow denies such claims.