U.S.-backed, Kurdish-led fighters captured the last town held by the Islamic State group on Friday, after days of intense battles in the militants' single remaining enclave in eastern Syria, activists said.

The fall of Hajin is a blow to the extremists. The town was their main stronghold in the last pocket of land they control in eastern Syria, near the Iraqi border. IS still holds some villages nearby.

The Kurdish-led Syrian Democratic Forces have been fighting to take Hajin and the surrounding villages in Deir el-Zour province for over three months. In the past weeks, the offensive intensified with the arrival of reinforcements from northern Syria.

The Britain-based Syrian Observatory for Human Rights said the SDF took Hajin early in the morning, after fierce fighting under the cover of airstrikes by the U.S.-led coalition. It said some IS fighters withdrew to the villages and that fighting is still going in the fields outside Hajin as SDF fighters chase the extremists.

Europe-based activist Omar Abu Layla of the DeirEzzor 24 monitoring group confirmed that the town was taken, adding that some IS fighters are still holed up in small pockets on the edge of Hajin.

Aby Layla said that in IS ranks, disagreements over hierarchy and posts between Iraqi and Syrian fighters helped "speed up the collapse" of IS defenses in Hajin.

Nuri Mehmud, spokesman of the Syrian Kurdish militia known as People's Protection Units or YPG — the main component of SDF — said "intense fighting" is still ongoing in small parts of Hajin.

The area was home to some 15,000 people, including 2,000 IS gunmen who fought back with counteroffensives and suicide attacks. Over the past days, hundreds of civilians were able to flee the enclave toward areas controlled by the SDF east of the Euphrates River and government-controlled regions on the river's west bank.

The Syrian Democratic Council, the political wing of the SDF, denounced Turkey's threat of a military operation against YPG and called on Syrians of all ethnic and religious groups to unite ahead of a possible Turkish attack.

Meanwhile, Turkish President Recep Tayyip Erdogan intensified his criticism of U.S. support for the Syrian Kurdish fighters, saying Friday that Turkey would clear the key northern town of Manbij. Over the summer, the two NATO allies had struck a "road map" for Manbij to remove YPG, which Turkey considers a terror organization linked to an insurgency within its own borders.

Erdogan argued the United States has not kept its promises to push YPG east of the Euphrates River.

"If you don't take them out, we will also enter Manbij," he said. American troops are stationed in Manbij, which was cleared of IS in 2016, and Washington and Ankara recently started joint patrols around the town.

Erdogan's threat comes days after he announced his military would launch a new cross-border operation into Syria "within a few days" to fight YPG east of the Euphrates.

On Thursday, a Turkish soldier was killed in the northwestern town of Afrin after an attack from nearby Tel Rifat. The Turkish military and allied Syrian opposition fighters took the town from the YPG earlier this year.

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Associated Press writer Zeynep Bilginsoy contributed to this report from Istanbul.