BEIRUT- The Syrian army and its allies have advanced to within 10 km (7 miles) of al-Mayadin, a military media unit run by the Lebanese Hezbollah group said on Friday, bringing them close to a city seen as the current main base of Islamic State.
They have won control of positions and heights parallel to the main road linking Deir al-Zor and al-Mayadin, located on the Euphrates in eastern Syria, the media unit said.
A war monitor, the Syrian Observatory for Human Rights, said on Thursday the army was only 6 km from al-Mayadin.
Islamic State has staged fierce counter attacks in central Syria in recent days, testing the army's control of an area seized in a months-long eastward offensive.
Backed by Russian air power, the army has continued its advance towards al-Mayadin from Deir al-Zor along the Euphrates valley.
In June, two US intelligence officials told Reuters that they believed Islamic State had moved most of its diminished command structure and propaganda team to al-Mayadin, southeast of its former capital of Raqqa.
The Observatory said on Friday there were clashes in several areas in eastern Deir al-Zor province. The Syrian military shelled al-Mayadin overnight and Syrian and Russian warplanes have conducted hundreds of strikes, it said.
Hezbollah, part of the military alliance supporting President Bashar al-Assad, said this week a senior commander had been killed in an Islamic State attack in Syria's central desert.
Helped by the Russian military and Iran-backed militias last month, the Syrian army's advance to Deir al-Zor lifted a three-year-long siege imposed by Islamic State on a government-held enclave in the city.
Islamic State has lost swathes of territory to the Syrian government and to US-backed Syrian militias that are waging separate campaigns against the jihadist group's last major strongholds in Deir al-Zor province.