The French government has confirmed it is preparing for French jihadists captured in northern Syria to return to France in the coming months following the departure of US troops from the region.

The question of what to do with foreigners who joined Islamic State has become increasingly vexed after the surprise announcement of a troop pullout by the US president, Donald Trump.

Until now, France’s position has been that French jihadists and Isis fighters captured abroad should be judged by local authorities – for example in Iraq, where some have been tried and convicted.

But the government is now making contingency plans on how to prevent French jihadists disappearing and going unaccounted for in north-east Syria as the US withdraws.

The French justice minister, Nicole Belloubet, told French radio on Thursday that the government would rather keep track of jihadists than risk them evading justice. “We’ve made a choice, which is that we prefer control, which means a return to France,” she said, although adding that the government was still studying “several options”.

French jihadists made up the largest contingent of European Isis recruits, and in 2015 and 2016 a cell of French and Belgian fighters who crossed from Turkey into Europe attacked the Paris Bataclan concert hall, national stadium and bars, as well as Brussels.

The French interior minister, Christophe Castaner, told French TV this week: “The Americans are leaving Syria. It’s important to keep that in mind.” He said there were a certain number of French jihadists “who are imprisoned because the Americans are there, and they will be freed. They will want to return to France.”

Castaner said all jihadists would be jailed immediately in France and face trial, but didn’t give more detail.

It is unclear how many French jihadist fighters are detained in northern Syria – whether it is dozens or more than 100. The French justice minister said a large number of those being held were in fact the young children of jihadist fighters. The issue of returning children is being dealt with case by case with the International Red Cross and French authorities.

The prime minister, Édouard Philippe, said he preferred that French jihadists were “judged, convicted and punished in France rather than disappearing to plan other actions, including against our country.”

Politicians on the right and far-right blasted the government for allowing French jihadists to return. Valérie Boyer of the rightwing party Les Républicains told parliament that the government must “prevent the return of jihadists who betrayed France and fought against our civilisation”. Another rightwing MP suggested what he called the “elimination” or targeted assassinations of French jihadists abroad.

A French foreign office spokesman said: “The government’s imperative is the security of French people.” On the situation in Syria, he said: “A part of the territory is still at war, in the north-east, and the American withdrawal risks leading to those terrorists dispersing. So we’re preparing for all eventualities in the north-east, including the eventuality of an expulsion.”