Islamic State militants recaptured Syria's ancient city of Palmyra on Sunday after briefly retreating in the face of heavy Russian airstrikes on their positions, Syrian State television said on Sunday.
The report quoted the governor of Homs and said Syrian forces were fighting to try and recapture the city.
Earlier, the British-based Syrian Observatory for Human Rights said the militants were back in control only hours after retreating to the orchards around Palmyra.
"Despite heavy losses in manpower and equipment, the terrorists are trying as hard as possible to secure a foothold inside the city," Interfax quoted a statement from Russia's monitoring center as saying. "Syrian troops are still fighting to defend Palmyra."
The center said Islamic State was drawing on "significant forces" from its strongholds in Raqqa and Deir al Zor.
Russia's Defense Ministry said its jets had launched 64 strikes and killed more than 300 militants during the operation, backing up the Syrian army.
Islamic State fighters had gained control of some oil and gas fields around the city during their advance which started on Thursday, the monitor said. They had also been pushing towards the nearby T4 air base - used by Russian forces supporting the Syrian army.
It was not immediately clear who now controlled the fields, including al Mahr and Jazal.
The city had been recaptured from the militants last March, in what was hailed as a major victory for the government and the biggest reversal for Islamic State in Syria since Russia's intervention, which turned the tide of the conflict in Assad's favor.
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