Syrian fighters backed up by artillery fire from a US-led coalition pressed their assault Monday to retake a last morsel of territory from the Islamic State group, a war monitor said.
More than four years after the extremists declared a "caliphate" across large parts of Syria and neighbouring Iraq, several offensives have whittled that proto-state down to a tiny holdout.
The Kurdish-led Syrian Democratic Forces (SDF) on Saturday announced the final push to expel hundreds of diehard jihadists from that patch in eastern Syria on the Iraq border.
The Syrian Observatory for Human Rights, a Britain-based monitor, said the alliance of Kurdish and Arab fighters was pressing on Monday in the face of tough obstacles.
"The SDF are advancing slowly in what remains of the IS pocket," Observatory chief Rami Abdel Rahman said.
But landmines, IS snipers, and tunnels the extremists have dug out for their defence are hindering the advance, he said.
SDF spokesman Mustafa Bali said there were "dozens of SDF hostages held by IS" inside their last foothold, but denied reports of executions.
The alliance has been battling to oust the jihadists from the eastern province of Deir Ezzor since September, backed by air power of the US-led coalition.
Screening for jihadists
Since December, tens of thousands of people, most women and children related to IS fighters, have fled to SDF territory.
US-backed forces near the village of Baghouz have screened the new arrivals, weeding out potential jihadists for questioning.
Another 600 people were able to reach SDF territory on Sunday after fleeing the fighting, the Observatory said.
Among them, were 20 suspected IS members, including two French women, seven Turks, and three Ukrainians, said the monitor, which relies on sources inside Syria.
The SDF -- which has said it expects the final offensive to be over in days -- announced Sunday that it had taken some 40 positions from the jihadists following direct combat involving light weapons.
The alliance had earlier said that up to 600 jihadists as well as hundreds of civilians could remain inside a patch four square kilometres (one mile square).
Spokesman Bali said IS leader Abu Bakr al-Baghdadi, the man who pronounced the cross-border "caliphate" in 2014, was not among them, and likely not in Syria.
At the height of their rule, the jihadists imposed their brutal interpretation of Islamic law on a territory roughly the size of Britain.
But military offensives in both countries, including by the SDF, have since retaken the vast bulk of their territory.
The jihadists however retain a presence in Syria's vast Badia desert, and have claimed a series of deadly attacks in SDF-held areas.
Planned US withdrawal
US president Donald Trump in December shocked Washington's allies by announcing a full withdrawal of US troops from Syria as IS had been "beaten".
But the US military warned in a report published this month that IS "could likely resurge in Syria within six to twelve months and regain limited territory" if sustained pressure is not maintained.
In January an IS suicide bomber attacked a US patrol in the northeastern city of Manbij, killing four Americans, five SDF fighters and ten civilians.
The losses were the worst combat losses for the US in war-torn Syria since it launched the coalition to fight IS in 2014.
Trump's decision to withdraw US troops has left Syria's Kurds scrambling for safeguards.
A US departure makes them more vulnerable to a long threatened attack by neighbouring Turkey, who considers Kurdish fighters to be "terrorists", and dashed their dreams of autonomy.
The Kurds have largely stayed out of Syria's nearly eight-year civil war, instead building their own semi-autonomous institutions in the northeast of the country.
But the expected US pullout has seen them grappling to mend ties with the Damascus regime, which is against Kurdish self-rule.
Syria's war has killed 360,00 people and displaced millions since it started in 2011 with the brutal repression of anti-government protests.