US-backed force attacks last IS pocket in eastern Syria
A US-backed militia alliance has begun what it says is the final stage of a campaign to clear the Islamic State (IS) group from north-eastern Syria.
The Syrian Democratic Forces launched a ground offensive on Monday against jihadist militants around Hajin, a town in the Middle Euphrates River Valley.
The international coalition backing the Kurdish and Arab fighters said they were expecting a "difficult fight".
Most are believed to be in an area stretching east from the Euphrates to the border with Iraq, about 25km (16 miles) away from Hajin, and in desert areas in the south and centre of the country, where the Syrian government is battling them.
Between 15,500 and 17,100 militants are thought to be based in Iraq, where IS no longer fully controls any territory. Many are hiding in the vast western desert.
At its peak in 2014, IS established a "caliphate" stretching across Syria and Iraq that was similar in size to the UK and ruled over more than 7.7 million people.
- IS 'releases new audio' of leader Baghdadi
- Up to 30,000 IS fighters in Syria and Iraq
- Islamic State group: The full story
SDF fighters launched the operation to drive IS "remnants" out of Hajin and the remaining countryside of eastern Deir al-Zour province after clearing the Baghuz and Dashisha areas - to the north and south - over the past four months.
An unnamed SDF commander told AFP news agency that at least 15 IS militants were killed in the first day of the Hajin offensive.
"The clashes will be fierce in Hajin because Daesh [IS] has reinforced their positions, but we will take control of it," the commander added.
The Syrian Observatory for Human Rights, a UK-based monitoring group, reported that the air strikes, artillery fire and ground attacks on IS positions were the heaviest in months.
The SDF also set up a humanitarian corridor for civilians to flee Hajin, it said.
"The multi-ethnic Syrian Democratic Forces remain committed to liberating the people of north-eastern Syria from [IS's] control and putting an end to the human suffering in the area," said Maj Gen Patrick Roberson, commander of the coalition's Special Operations Joint Task Force.
"Moving forward, we will continue co-ordination with the SDF and other partners to promote regional security and stability that will ensure a lasting defeat of [IS]."
Last month IS released an audio message purportedly from its leader, Abu Bakr al-Baghdadi, in which he declared that the caliphate would "remain", adding: "IS is not confined to Hajin."
Baghdadi's location is not known, but a coalition spokesman told AFP that it believed some high-value IS targets could still be present in Hajin.
In a separate development on Tuesday, the Syrian Observatory for Human Rights said at least 21 pro-government fighters had been killed in an ambush by IS militants in a remote Tulul al-Safa area of Suweida, in the south-west of the country.
Syrian state media reported fierce clashes in the area, and said government aircraft and artillery had bombed IS "hideouts", killing or injuring scores of militants.