BRUSSELS (AFP) - Belgium must do everything it can to ensure the safe return of Belgian militants' children being held in Kurdish-controlled camps in northern Syria, Prime Minister Alexander de Croo said on Thursday (March 4).

De Croo warned that conditions in the two camps, packed with detainees since the territorial defeat of the Islamic State in Iraq and Syria (ISIS) group, were deteriorating and those under 12 years old must be allowed to come home.

He warned of the risk of the children being radicalised in the camps.

"In these camps there are the terrorists of tomorrow and we cannot permit that," he told parliament.

"These children, we must do all we can to get them out," he said.

The prime minister said there were around 30 children under the age of 12 concerned.

He also said the situation of 13 Belgian women being held in the camps would be examined "case by case", adding that nine of them had already been convicted by Belgian courts and four were targets of international arrest warrants.

"It's clear the situation of the mothers is also of concern," he said.

A UN expert in early February warned that "inhumane" treatment was meted out in the camps, where 64,000 people were being held, most of them women and children.

Belgium and France are among the main European countries from which the biggest number of Islamic militant fighters left to join ISIS when Syria's war broke out in 2011.

Since then, both countries have been targeted in attacks claimed by ISIS, including one in Brussels in 2016 in which 32 were killed, and one in Paris in 2015 in which militants murdered 130 people.