Migrants wait to board buses on a field near the village of Babska, Croatia September 23, 2015.

Dutch authorities said on Thursday there was no sign of militant groups systematically using Europe’s asylum provisions as a way of smuggling attackers into Europe disguised as refugees.

Far-right politicians in the Netherlands and elsewhere in Europe have suggested in recent months that the hundreds of thousands of people fleeing war and poverty in the Middle East and Africa pose a national security threat.

But, echoing scepticism expressed by other intelligence services, a spokeswoman for the AIVD intelligence agency said there was no evidence that militant organisations like the Islamic State of Iraq and Syria (ISIS) were infilitrating fighters across Europe’s southern and south-eastern borders.

“There are no structural signals of refugees coming in with terrorist motives,” a spokeswoman for the AIVD intelligence agency told Reuters. “It is possible that individuals may use it (the route) but we don’t see groups coming in.”

Germany‘s domestic intelligence service, however, warned on Tuesday that radical Islamists posing as humanitarian helpers could try to recruit young refugees arriving in the country.

Dutch anti-Islamic politician Geert Wilders recently referred to the influx as an “Islamic invasion”, saying that thousands of Islamist militants were concealed among those fleeing conflict in Syria and Iraq.

A poll this week showed his far-right populist Freedom Party would nearly double its seats, from 12 to 29 in the 150-member parliament, if elections were held now.

More than half of Dutch voters oppose a European deal under which the country will admit an additional 7,000 refugees.

The Dutch government has been stepping up security measures amid growing concern at the threat of attacks by returning militants and plans to grant sweeping cable-tapping powers to intelligence agencies.