Kurdish-led forces made fresh gains against jihadists defending their eastern Syria stronghold Monday, forcing hundreds of people to flee the fighting, a war monitor said.
The Syrian Democratic Forces, with aerial support from the US-led coalition, closed in on the two main spots where jihadists are digging their heels in, the Syrian Observatory for Human Rights said.
"There is currently fighting around the villages of Al-Shaafa and Sousa," said Rami Abdel Rahman, head of the Britain-based monitor.
The two villages are the main hubs in what is left of the Islamic State group's last pocket in the Euphrates River valley, near the Iraqi border.
"The latest developments are in favour of the SDF and it appears the Islamic State may collapse soon," Abdel Rahman said.
An SDF spokesman, Kino Gabriel, said the Kurdish-Arab alliance was able to repulse several jihadist attacks and was now advancing from three different directions.
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A few hundred holdout fighters are defending the last rump of the jihadist organisation's self-proclaimed "caliphate", which once covered territory the size of Britain.
The fighting comes days after US President Donald Trump announced his decision to pull US troops out, a move many within his own administration feared would weaken the fight against IS.
The SDF reported in a statement on Sunday that it had evacuated 1,000 civilians from the area where the fighting was taking place.
The Observatory said a total of more than 5,000 people were able to flee the IS pocket since the SDF took Hajin, which had been the main hub in the jihadist's Euphrates pocket, on December 14.
Abdel Rahman said most of them were women and children but he added that some fighters were trying to blend in with civilians, forcing the SDF to screen the evacuees at the Omar oil field.
The fall of Al-Shaafa and Sousa will cap a years-long multi-national effort to smash the sprawling pro-state IS declared over parts of Syria and Iraq in 2014.
If the jihadists lose these two villages, they will no longer control any populated areas in Iraq or Syria and will have fully reverted to being a clandestine group hiding in desert areas.