AMMAN - The Syrian army fired heavy artillery on the city of Deir al-Zor on Thursday, killing at least 11 people after a ground offensive met heavy resistance in the capital of the oil-producing province, opposition sources said.

The overnight barrage from nearby hills followed the withdrawal of hundreds of troops backed by tanks that had entered the city on Wednesday to root out rebels, the sources said. About 200 people were wounded in the shelling, they said.

A main oil pipeline from Deir al-Zor province feeds Syria's two refineries, in the city of Homs and an export terminal on the Mediterranean. Large swathes of the province have fallen into rebel hands in the past few months.

"Deir al-Zor was hit by a few artillery rounds during the first army attack on the city back in August, but this is the first time we have seen sustained shelling," said a source at a hospital in the city, who spoke on condition of anonymity.

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