BEIRUT (Reuters) - The Syrian army and its allies have captured areas of Islamic State-held al-Mayadin in eastern Syria, a Hezbollah-run military news outlet reported on Thursday, in an advance into the jihadist group’s main urban base of operations in Syria.

Backed by Russia, Iran and Shi’ite militias, the Syrian army encircled the militants in al-Mayadin on Sunday.

In June, two U.S. 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.