BAGHDAD (Reuters) - U.S.-backed Syrian Democratic Forces (SDF) handed over more than 150 Iraqi and other foreign Islamic State fighters to Iraq on Thursday.

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The handover was the first of several, two Iraqi military sources told Reuters, under an agreement brokered to handover a total of 502 fighters.

“The majority of the fighters are Iraqi,” said a military colonel whose unit is stationed at the Syrian border. “But we have a few foreigners.”

The mayor of Iraqi border town Al-Qaim, Ahmed al-Mahallawi, said some fighters’ families were also transferred.

“Early this morning, 10 trucks loaded with Daesh fighters and their families were handed over by SDF forces to the Iraqi army,” he said, using the Arabic acronym for Islamic State.

“The majority of them are Iraqis and the convoy was under maximum security protection headed to the Jazeera and Badiya military headquarters.” Both bases are located in Anbar province.

The SDF and the U.S.-backed coalition could not immediately be reached for comment.

News of the handover came as U.S.-backed forces were readying for an assault on the militant group’s final enclave in eastern Syria. The last civilians are expected to be evacuated on Thursday, to clear the way for the assault, the SDF said.

Around 800 of foreign jihadist fighters who joined Islamic State, including many Iraqis, are being held in Syria by the SDF, the group said. More than 2,000 family members are also in camps, with dozens more arriving each day.

Their fate has become more pressing in recent days as U.S.-backed fighters planned their assault to capture the last remnants of the group’s self-styled caliphate.

On Tuesday, Iraqi Prime Minister Adel Abdul Mahdi said Iraq was carefully monitoring the situation at its Syrian border amid concerns that the remaining Islamic State fighters could stream across the border.

The militant group still poses a threat in Iraq and some western officials believe that the group’s leader, Abu Bakr al-Baghdadi, may still be hiding there.