Syrian fighters backed by artillery fire from a US-led coalition battled a fierce jihadist counteroffensive as they pushed to retake a last morsel of territory from the Islamic State group in an assault lasting days.
A war monitor said a coalition air strike killed 16 civilians including seven children trying to flee the holdout on Monday, but the US-led alliance was not immediately available for comment.
More than four years after the extremists declared a "caliphate" across large parts of Syria and neighbouring Iraq, several offensives have whittled that down to a tiny scrap of land in eastern Syria.
The final push to expel hundreds of diehard jihadists from that patch on the Iraq border was announced Saturday by the Kurdish-led Syrian Democratic Forces (SDF).
On Monday the US-led coalition maintained a steady beat of bombings on the area as the SDF faced ferocious resistance.
The sound of explosions echoed dozens of kilometres (miles) away and columns of dark grey smoke could be seen from SDF territory.
"Heavy clashes are ongoing to pressure IS into surrendering," said Rami Abdel Rahman, chief of Britain-based monitor the Syrian Observatory for Human Rights.
The Observatory said 12 SDF fighters and 19 jihadists were killed in the fighting on Monday.
SDF spokesman Mustafa Bali said the force responded after IS launched a counterattack earlier in the day. He also said there were "dozens of SDF hostages held by IS" inside their last foothold, but denied reports of executions.
US President Donald Trump said on Monday that the coalition may declare victory over IS in the region in the coming days.
"Our brave warriors have liberated virtually 100 percent of ISIS (territory) in Iraq and Syria... soon it will be announced, soon, maybe over the next week, maybe less, but it will be announced we have 100 percent," he told a rally in the US city of El Paso.
- French women -
Backed by coalition air strikes, the SDF alliance has been battling to oust the jihadists from the eastern province of Deir Ezzor since September.
Since December, tens of thousands of people, most women and children related to IS fighters, have fled the shrinking jihadist holdout into SDF territory.
US-backed forces have screened the new arrivals, weeding out potential jihadists for questioning.
On Monday, dozens of coalition and SDF fighters were stationed at a screening point for new arrivals from IS areas.
Coalition forces stood over about 20 men who were crouching on the ground.
Two French women told AFP they paid smugglers to take them out of the battered IS-held holdout of Baghouz, but Iraqi jihadists had prevented other foreigners from leaving.
"They said only the Syrians and Iraqis can be smuggled out," said one of the women, who said her first name was Christelle, from the city of Bordeaux.
The Observatory said 600 people including around 20 suspected jihadists fled IS areas overnight.
On Saturday, the alliance had said up to 600 jihadists as well as hundreds of civilians could remain inside the IS patch of four square kilometres (one square mile).
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.
- Planned US withdrawal -
At the height of their rule, IS 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.
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 12 months and regain limited territory" if sustained pressure is not maintained.
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, which considers Kurdish fighters to be "terrorists", and dashes 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.