LILLE, France – Two Belgian policemen were arrested for helping a group of migrants return to France after they wound up in Belgium by mistake while heading to Calais, officials said Thursday.

French Interior Minister Bernard Cazeneuve summoned Belgium’s ambassador to France, Vincent Mertens de Wilmars, to "ask for an explanation (and) express his displeasure", the ministry said.

The Belgian officers were arrested by their French counterparts in the border town of Nieppe late Tuesday after they brought the 13 Iraqi and Afghan migrants across the frontier.

French police said the migrants had originally been in a truck believing they were heading for Calais – the northern French port from where they wanted to try to travel on to Britain – but got out after realising that they had crossed into Belgium.

The Belgian police then picked them up on the side of the road, according to one of the Belgian officers, Georges Aeck.

He told Belgian broadcaster RTBF: "We didn’t want to leave them... on the side of the road to walk to the border.

"So we took them... in the direction they wanted to go."

The Belgian police took the migrants back to France in a police van, "but without respecting the re-admission procedure under which you have to inform the authorities," a police source said.

French authorities expressed "their strongest condemnation after this initiative, which does not conform to the normal work practices agreed between France and Belgium."

An official French source said the two Belgian police officers had been questioned "as witnesses" and were able to leave the French police station during Monday night.

’Border not very visible’

Belgium however denied that Cazeneuve had summoned its ambassador in Paris after the incident.

"The precise rule is that you bring refugees to the border. The problem here is that the boundary in that street was not very visible," Belgian Interior Minister Jan Jambon told public broadcaster RTBF.

"This is a minor incident, not a big thing, They entered French territory because they didn’t see exactly where the border was," he added.

The Belgian police union on Wednesday said the French police had handcuffed their Belgian colleagues before questioning, a claim denied by French authorities, and the union took it back.

Union president Vincent Gilles said about the circumstances of the Belgian police arrest that "there was nothing bad to say about our French colleagues."

A police source said the incident was "a first" and that the Belgian and French police "get along well."

The migrants were taken to a border police station in the northern French city of Lille.

Three minors were placed in the care of local authorities and the adults have been temporarily detained while their status is assessed.

Calais is a magnet for migrants who try to board lorries there to reach Britain.

The migrant crisis and immigration are hot topics in France seven months ahead of presidential elections.

The French government has begun dismantling the sprawling migrant camp in Calais known as the "Jungle", a squalid collection of tents and temporary shelters holding between 7,000 and 10,000 people.

More than 300,000 people have crossed the Mediterranean so far this year to seek asylum or a better life in Europe, according to the UN refugee agency UNHCR. — AFP