The Syrian Democratic Forces (SDF) this week launched a new offensive against holdouts from the "Islamic State of Iraq and Syria" (ISIS) in eastern Syria, AFP reported Tuesday (May 8th).

Kurdish members of the Arab-Kurd alliance had quit the Middle Euphrates River Valley in February after Turkey sent troops into Syria and launched an operation against the SDF in its Afrin enclave.

But the SDF last week announced it was relaunching efforts to clear ISIS from the few areas in Syria where they maintain a presence, including in the eastern province of Deir Ezzor near the border with Iraq.

"This week, following an increase in coalition strikes against the final ISIS controlled areas in Syria, the SDF resumed offensive operations to clear the final ISIS-held territory in eastern Syria," said British Army Maj. Gen. Felix Gedney, a deputy commander of the coalition.

The first phase of operations aims to secure the south-east portion of the Syria-Iraq border in co-ordination with the Iraqi security forces, Gedney said.

He did not say how many ISIS fighters remain, though noted that local extremists are abandoning the fight, causing tension among those remaining.

"Observations from eastern Syria suggest that morale among ISIS fighters is sinking," Gedney said.

"Frictions are mounting between native- and foreign-born ISIS fighters as ISIS's privileged leadership continues to flee the area leaving fighters with dwindling resources and low morale. ISIS fighters continue to surrender rather than face certain death."

More than 400 ISIS fighters are now in SDF custody, he added.