US-backed Syrian Democratic Forces said the "final battle" has begun to oust the Islamic State group from the last scrap of territory it holds in eastern Syria.
IS overran large parts of the country and neighboring Iraq in 2014, declaring a "caliphate" there, but various military offensives have reduced it to a fragment.
Backed by air strikes of the US-led coalition against IS, the Kurdish-Arab alliance has in recent months cornered the jihadists in a final pocket of territory in Syria's eastern province of Deir Ezzor.
After a pause of more than a week to allow civilians to flee, the SDF said Saturday it had resumed the fight to seize the last four-square-kilometer patch from the jihadists.
"The SDF have launched the final battle to crush IS . . . in the village of Baghouz," it said. "After 10 days of evacuating more than 20,000 civilians . . . the battle was launched tonight" to wipe out the last remnants of the organization.
SDF spokesman Mustafa Bali told media: "The battle has started. This battle will be sealed in the coming days."
Bali said there could be up to 600 IS fighters still inside the pocket, most of them foreigners. Hundreds of civilians are also believed to be inside.
At the height of its rule, IS controlled territory the size of Britain. But a series of separate military operations, including by the SDF, have left its proto-state in tatters. The coalition said the "caliphate" had massively shrunk.
Major General Christopher Ghika, the coalition's deputy commander, described the size of the last IS pocket as "now less than 1 percent of the original caliphate."
Despite its "caliphate" being on the brink of collapse, IS still retains a presence in Syria's vast Badia desert, and has carried out deadly attacks in SDF-held territory.
The Kurdish People's Protection Units, known as YPG, and their female equivalent, the Women's Protection Units, have formed the backbone of the SDF.
In the northeastern Kurdish-majority city of Qamishli on Saturday, SDF fighters stood to attention at the funeral of a YPJ fighter who died fighting IS.
Syria's war has killed more than 360,000 people and displaced millions since it erupted in 2011 with the brutal repression of anti-government protests.
The country's Kurds have largely stayed out of the conflict, instead developing semi-autonomous institutions in parts of the country's northeast under their control.
Neighboring Turkey sees Syrian Kurdish fighters as "terrorists," and has repeatedly threatened to attack YPG-held areas along its southern border.
The US military presence in Syria has offered the Kurds a measure of protection against any Turkish offensive.
But in December, Washington announced it would pull out all its troops from Syria, sending Kurdish authorities scrambling to mend fences with the regime in Damascus.