ISTANBUL — An armed opposition group receiving international support has made significant gains in Syria recently against the Islamic State (IS) in the southern desert area and close to the capital.

The core of the group — called Jaish Usud al-Sharqiya (Lions of the East Army) — is from Syria’s easternmost province, Deir ez-Zor. Its leader, Tlass al-Salama, told Al-Monitor that the group's main aim is to return to the area, which will almost certainly be IS’ last stronghold in the country.

In the early morning of April 9, the al-Tanf base on the border of Jordan and Iraq, which is used by the group as well as US and British forces, suffered a major IS attack; the attack followed US strikes on a Syrian air base in Idlib.

“Coalition and partnered forces defended against the [IS] attack with direct fire before destroying enemy assault vehicles and the remaining fighters with multiple coalition air strikes,” a coalition statement reported. “VSO (Vetted Syrian Opposition) forces focus on conducting operations to clear [IS] from the Hamad Desert and have been instrumental in countering the [IS] threat in southern Syria.”