Syria's army declared victory over Islamic State on Thursday, saying its capture of the jihadists' last town in the country marked the collapse of their project in the region.
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The army and its allies are still fighting Islamic State in desert areas near Albu Kamal, the last town the militant group had held in Syria, near the border with Iraq, the army said.
But the capture of the town ends Islamic State's era of territorial rule over the so-called caliphate that it proclaimed in 2014 across Iraq and Syria and in which millions suffered under its hardline, repressive strictures.
Yet after ferocious defensive battles in its most important cities this year, where its fighters bled for every house and street, its final collapse has come with lightning speed.
Instead of a battle to the death as they mounted a last stand in the Euphrates valley towns and villages near the border between Iraq and Syria, many fighters surrendered or fled.
In Albu Kamal, the jihadists had fought fiercely, said a commander in the pro-Syrian government military alliance. But it was captured the same day the assault began.
This sealed "the fall of the terrorist Daesh organization's project in the region", an army statement said, using an Arabic term for Islamic State.
The fate of its last commanders is still unknown -- killed by bombardment or in battle, taken prisoner but unidentified, or hunkered into long-prepared hideouts to plot a new insurgency.
The Britain-based Syrian Observatory for Human Rights says government forces and allied troops, including Iraqi fighters, are combing Boukamal, a strategic town on the border with Iraq, on Thursday after ISIS militants withdrew.
Syrian pro-government media say Syrian troops had clashed with remnants of IS militants in the town after they entered it late Wednesday. On Thursday, they declared the town totally free of the militants.
The fall of Boukamal means remaining IS militants are currently holed up in small towns and villages along the border with Iraq and in the Syrian desert.
The last appearance of Abu Bakr al-Baghdadi, who declared himself caliph and heir to Islam's historic leaders from the great medieval mosque in Iraq's Mosul, was made in an audio recording in September.
"Oh Soldiers of Islam in every location, increase blow after blow, and make the media centers of the infidels, from where they wage their intellectual wars, among the targets," he said.
Mosul fell to Iraqi forces in July after a nine-month battle. Islamic State's Syrian capital of Raqqa fell in October to the Syrian Democratic Forces (SDF), a U.S.-backed alliance of Kurdish and Arab militias, after four months of fighting.
But all the forces fighting Islamic State in Syria and Iraq expect a new phase of guerrilla warfare, a tactic the militants have already shown themselves capable of with armed operations in both countries.
Western security chiefs have also said its loss of territory does not mean an end to the "lone-wolf" attacks with guns, knives or trucks ploughing into civilians that its supporters have mounted around the world.