The Daesh terrorist group used at least 10 suicide bombers on Friday in a massive attack on Albu Kamal, in which they retook parts of the eastern Syrian town, a monitor said.

At least 25 regime and allied fighters were killed in the terrorists' offensive, one of the largest this year, the Syrian Observatory for Human Rights said.

"It's the biggest attack on Albu Kamal since they lost it" in November 2017, said Rami Abdel Rahman, the head of the Britain-based Observatory.

"IS now controls several parts of the city. Fighting is ongoing in the center," he added, using an alternate acronym for the terrorist group.

Albu Kamal lies on the border with Iraq in Syria's Deir el-Zour province, about 440 kilometers (270 miles) east of the capital Damascus.

The area was the heart of the once sprawling, self-styled "caliphate" Daesh proclaimed in 2014 and its recapture by pro-regime forces last year was the final nail in the proto-state's coffin.