ANKARA (Reuters) - Turkish Defense Minister Hulusi Akar said on Monday Syrian Kurdish YPG fighters had emptied a jail holding Islamic State prisoners in a part of Syria where Ankara is mounting an offensive, and that the prisoners there had been abducted.

Turkey launched a cross-border operation against the YPG militia in northeastern Syria last week, after U.S. President Donald Trump decided to withdraw forces from two posts in the area in a move that drew strong international criticism.

The Turkish assault has prompted alarm that it could allow Islamic State (IS) militants to escape Kurdish-run prisons in northern Syria and regroup. Ankara has dismissed those concerns.

Turkey’s stated objective is to clear its southern frontier region of the YPG, which it views as a terrorist organization, and form a “safe zone” 30 km (20 miles) into Syrian territory where it wants to settle millions of Syrian refugees. Ankara also pledged to take responsibility for IS militants within the “safe zone”, but said it would not be accountable for others.

Speaking to reporters in Ankara on Monday, Akar said the YPG had emptied the only Islamic State prison that Turkish forces had so far reached in the envisaged “safe zone” area, and that the inmates had already been removed.

“As you know, there is a prison issue on this Daesh (Islamic State) topic. We are determined to show the utmost effort on these prisons. However, there was only one prison in our region, a Daesh prison,” Akar said.

“When we went there, we saw that it had been emptied by the YPG and the Islamic State militants there had been abducted. We determined this through photographs and film, talked to our counterpart, and will continue to do so,” he added.

Akar did not say how many prisoners were believed to have been taken from the jail, nor did he elaborate on who had taken the prisoners and where. There was no immediate YPG comment.

Trump, providing no evidence, tweeted on Monday that Kurdish forces might be freeing IS prisoners deliberately to lure U.S. troops back into the region. Escaped fighters could be “easily recaptured by Turkey or European Nations from where many came, but they should move quickly”, Trump said.

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Later on Monday, Turkish media broadcast footage of what it said was the prison emptied by the YPG in central Tel Abyad, along the Turkish border. The footage showed Turkish soldiers roaming through an empty building with jail cells built inside.

The fighting has raised Western concerns that the Kurds, holding large tracts of northern Syria previously controlled by Islamic State, would be unable to keep thousands of jihadists in jail and tens of thousands of their family members in camps.

The region’s Kurdish-led administration said 785 IS-affiliated foreigners escaped a camp at Ain Issa at the weekend. The UK-based war monitor Syrian Observatory for Human Rights, citing sources in the camp, said around 100 people had escaped.

President Tayyip Erdogan dismissed the reports on Sunday, saying that accounts of escapes by Islamic State prisoners were “disinformation” aimed at provoking the West.