Capture of Albu Kamal is last in string of setbacks that has seen IS lose its urban bastions of Mosul and Raqqa within weeks
Syrian troops and allied militiamen on Thursday expelled Islamic State (IS) group fighters from Albu Kamal, the last significant town IS held in its disintegrating "caliphate".
The group's latest rout left them with only the dregs of a self-styled "state" that once spanned substantial territory across Iraq and Syria, with surviving IS militants melting away into desert hideouts.
Anti-IS forces stormed the town just across the border from Iraq on Wednesday, and while fighting was initially reported as fierce, the outcome of one of IS's last major battles was never in doubt.
"Our armed forces units, in cooperation with allied and auxiliary forces, have liberated the town of Albu Kamal in Deir Ezzor province," a statement carried by the official SANA news agency said.
"Albu Kamal's liberation is very important because it means the failure of the IS terrorist group in the region," the army statement said.
The Syrian Observatory for Human Rights, a Britain-based monitor of the war, said much of the fighting had been done by allied militias rather than the regular army.
The capture of Albu Kamal was the last in a series of setbacks that saw IS lose its urban bastions of Mosul and Raqqa within a few weeks and its embryonic state shrink to a rump.
Leading the battle for the town were the Lebanese Shia militant group Hezbollah and advisers from Iran's elite Revolutionary Guards, as well as fighters from mostly Shia Iraqi militias, according to Observatory chief Rami Abdel Rahman.
He said that even as IS still controlled half of the town and fighting raged earlier on Thursday, the militants retained one escape route to the north.
Abdel Rahman confirmed that Albu Kamal had been fully retaken, saying: "IS withdrew to desert areas in eastern Deir Ezzor" province, where they are likely to encounter US-backed Kurdish-led fighters.
The group's flight from the town, where IS leaders used to meet and were once considered untouchable, caps a process which has seen the group relinquish any ambition as a land-holding force and return to the desert to fight a clandestine guerrilla war.
Many of the group's top leaders have been killed as Syrian and Iraqi forces with backing from Russia, Iran and a US-led coalition rolled back the territorial gains that saw the militants declare a "caliphate" roughly the size of Britain in 2014.
But the whereabouts of the first among them, self-proclaimed "caliph" Abu Bakr al-Baghdadi, remains unclear. He has been reported killed or wounded many times, but IS has never offered any confirmation.
The capture of the group's last urban stronghold had appeared to be a matter of days after Syrian forces last week retook provincial capital Deir Ezzor and Iraqi forces reconquered Albu Kamal's twin town of Al-Qaim, just over the border.
There was little to slow the advance of the Syrian army and its allies after their victories farther up the Euphrates Valley, but while the military phase of the fight against IS may be nearing an end, the humanitarian crisis it sparked is in full swing.
"In the last few weeks, an estimated 120,000 people were displaced from Albu Kamal," the United Nations' humanitarian affairs office in Damascus said.
IS still has a small presence in the east of Homs province, in the southern outskirts of Damascus and in the southern province of Daraa.
It also holds the small Iraqi town of Rawa down the Euphrates Valley from Al-Qaim.
A rival militant alliance led by Al-Qaeda's former Syria affiliate controls much of the northwestern province of Idlib and adjacent areas, as well as pockets of territory elsewhere.
It has come under attack by Russian-backed government forces and by Turkish-backed rebels.
More than 330,000 people have been killed in Syria since the conflict began with anti-government protests in March 2011, which then spiralled into a complex, multi-front war that drew in militants and armed forces from around the region and beyond.