U.S.-backed militias said they had launched their final assault on Syria's Raqqa on Sunday after a convoy of Islamic State fighters left the city, leaving only a hardcore of jihadists to mount a last stand.
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"The battle will continue until the whole city is clean," said a statement by the Syrian Democratic Forces, a U.S.-backed alliance of Kurdish and Arab militias.
An SDF spokesman told Reuters that a total of 275 Syrian Islamic State fighters have departed the city, leaving behind around 200 to 300 mostly foreign fighters. Almost all civilians in Raqqa's Islamic State enclave have been allowed safe passage out as part of the deal.
Raqqa's fall to the SDF now looks imminent after four months of battle.
"We still expect there to be difficult fighting," said Colonel Ryan Dillon, spokesman for the U.S.-led international coalition backing the SDF in the war against Islamic State.
Raqqa was the first big Syrian city to fall to Islamic State as it declared a "caliphate" and rampaged through Syria and Iraq in 2014, becoming an operations centre for attacks abroad and the stage for some of its darkest atrocities.
But Islamic State has been in retreat for two years, losing swathes of territory in both countries and forced back into an ever-diminishing foothold along the Euphrates river valley.
"Last night, the final batch of fighters (who had agreed to leave) left the city," said Mostafa Bali, an SDF spokesman.
Before the convoy left, the coalition estimated that about 300 to 400 fighters remained.
The convoy would head to the remaining Islamic State territory in eastern Syria and included about 400 civilians along with the fighters, Alloush had said on Saturday.
Bali described the civilians who left with Islamic State fighters in the convoy as human shields. The jihadists had refused to release them once they left the city as agreed, wanting to take them as far as their destination to guarantee their own safety, he said.
Such withdrawals of fighters along with groups of civilians have grown commonplace in Syria's six-year war, as a way for besieging forces to accelerate the fall of populated areas.
In previous evacuations, including by Islamic State, the civilians usually included family members of the fighters.
The agreement was brokered by the Raqqa Civil Council and tribal elders to "minimise civilian casualties", the coalition said on Saturday. Tribal leaders from Raqqa said they sought to prevent bloodshed among civilians still trapped in the city.
The SDF's decision to hasten the battle's end by allowing Islamic State fighters to leave Raqqa was at odds with the stated wishes of the U.S.-led coalition that backs the militias with air strikes and special forces.
Dillon said on Sunday it was not involved in the evacuation but added: "We may not always fully agree with our partners at times. But we have to respect their solutions."
In August, the coalition spent weeks preventing a convoy of Islamic State fighters evacuated from an enclave on the Syrian-Lebanon border from reaching jihadist territory in eastern Syria.
The SDF announced the start of the battle for Raqqa on June 6 after a months-long campaign to isolate the city against the north bank of the Euphrates.
Islamic State, then known as Islamic State in Iraq and the Levant, had captured the city in January 2014, seizing it from rebel factions which had ousted the Syrian army a few months earlier.
As the group became more entrenched in Syria and Iraq leading up to its capture of Mosul in June that year, Raqqa became its most important centre, and its series of victories were celebrated in a massive parade through the city.
Many of its top leaders were at times based there, and former hostages said Mohammed Emwazi, better known as Jihadi John, imprisoned them along with those he later executed, in a building near an oil installation near the city.
The group killed dozens of captured Syrian soldiers there in July 2014 and it was also the site of a slave market for Yazidi women captured in Iraq and given to fighters.
The coalition has said Raqqa was a hub for attacks abroad, and in November 2015, after militants killed more than 130 people in Paris, France launched air strikes on Islamic State targets inside Raqqa.
But the group is now in disarray. In Syria it does not only face the U.S.-backed SDF offensive but a rival one by the Syrian army supported by Russia, Iran and allied Shi'ite militias.
A Syrian military source said on Saturday the army had captured the city of al-Mayadin in the Euphrates valley, leaving Islamic State only a few more towns and villages, and areas of the surrounding desert, in Syria.
But the battle for Raqqa has come at great cost to its people. Much of the city has been pulverised by the intense coalition air strikes and by the months of street-to-street fighting. Thousands of people have fled as refugees and hundreds of civilians have died.