The U.S. State Department called on countries to take in and prosecute hundreds of foreign fighters captured by America's Kurdish allies in Syria as the United States withdraws troops from the country.

The department's spokesman, Robert Palladino, did not say how many prisoners were detained by the Syrian Democratic Forces — an alliance of militias dominated by the Kurdish YPG — but U.S. officials believe they number about 850.

The United States has long said it wants to see the fighters returned to their countries of origin for prosecution.

"The SDF has demonstrated a clear commitment to detain these individuals securely and humanely," Palladino said in a statement.

"The United States calls upon other nations to repatriate and prosecute their citizens detained by the SDF," he added.

Washington on Wednesday hosts a meeting of about a dozen coalition partners fighting Islamic State in Syria.

Questions have arisen about what the SDF would do with the prisoners since President Donald Trump's announcement in December that the United States would withdraw all of its 2,000 troops from Syria.

The announcement stunned allies, especially the SDF, which has been among the most effective against Islamic State.

FILE - An Iraqi student walks past a school wall c FILE - An Iraqi student walks past a school wall covered with drawings showing how Islamic State militants executed their prisoners in Mosul, Iraq, April 30, 2018. FILE - An Iraqi student walks past a school wall covered with drawings showing how Islamic State militants executed their prisoners in Mosul, Iraq, April 30, 2018.

Meanwhile, the Syrian Observatory for Human Rights, the U.K.-based war monitoring group, said in December that Islamic State militants had executed nearly 700 prisoners in nearly two months. The prisoners were among 1,350 civilians and fighters that Islamic State has been holding near the Iraqi border.