President Trump on Friday renewed his threat to dump ISIS prisoners back to the European countries they hailed from — saying the US would drop them at the border and the Europeans will “have to capture them again.”

“I defeated the caliphate. When I came, the caliphate was all over the place. I defeated the caliphate, ISIS, and now we have thousands of prisoners of war, ISIS fighters that are prisoners of war, and we’re asking the countries from which they came … from Europe, We’re asking them to take back these prisoners of war,” the president told reporters alongside Australian Prime Minister Scott Morrison at the White House.

“So far, they’ve refused, and at some point, I’m going to have to say, ‘I’m sorry, you either take them back or we’re going to let them go at your border.’ And if they don’t take them back, we’re going to probably put them at the border and then they’ll have to capture them again,” Trump continued.

The commander in chief’s comments came after he was asked about possible retaliation against Iran.

He replied by extolling increased military spending on his watch before turning his attention to prisoners captured by the US and their allies in the fight against ISIS, which had established a caliphate in large swaths of Iraq and Syria.

“They came out from Germany, they came out from France. The United States is not going to have thousands and thousands of people that we’ve captured, stationed at Guantanamo Bay, held captive at Guantanamo Bay for the next 50 years and us spending billions and billions of dollars,” Trump said.

“We’ve done Europe a tremendous favor. they mostly come out of Europe. So they have to make their decision. Otherwise, we’re releasing them at the border.”

The president’s remarks echoed comments he made in April and again last month, but it was unclear if he had a timeline for when the prisoners could be moved.

The Syrian Democratic Forces, a US-backed Kurdish group, has captured roughly 9,000 ISIS fighters. It was unclear how many hailed from Europe or other countries outside of the region.

Officials in a handful of European countries have called for stripping ISIS members of their passports, including Denmark, Switzerland and the United Kingdom.