ROME, April 13 (Xinhua) -- Italian judicial authorities on Friday issued an order of European investigation against French police officers that crossed the border to conduct checks on migrants on Italian territory last month.

The incident occurred in the border resort of Bardonecchia in the province of Turin -- some 20 kilometers from the first French town -- on March 30.

Chief prosecutor in Turin Armando Spataro explained the order of investigation involved five officers of the French custom police, who physically carried out the search on migrants.

"Beyond any (cross-border) agreement, the French custom authority had no right to carry out that sort of activities on Italian territory, especially as it did not ask help or intervention from Italian police," Spataro told a press conference later broadcast by local media.

The five French officers were under investigation on suspicion of complicity in unlawful entry of property and illegal search, according to the prosecutor. The order of investigation was sent to the French liaison magistrate in Italy.

"In this order, we ask the French authority in charge to unveil the identity of the five officers, and to question them at the presence of the Turin prosecutors," Spataro explained. "We also ask to be sent all of the papers related to the activity of the suspects," he added.

A diplomatic row between Italy and France was sparked by the episode, which saw French custom police entered a center for migrants run by non-governmental group "Rainbow For Africa" in the train station of Bardonecchia.

Set up in cooperation with local authorities, the clinic aims to provide first aid, counselling, and night refuge to migrants trying to cross the Alps mountain chain, which marks the French-Italian border.

The French officers got into the NGO's center, and ordered a Nigerian citizen to undergo a urine test on suspicion of drug trafficking. The test was negative. As the Turin chief prosecutor later clarified on Friday, the Nigerian man was a legal migrant in possession of a regular residence permit.

On March 31, the day after the incident, the Italian Foreign Affairs Ministry summoned the French ambassador to Rome, Christian Masset, for clarifications.

France said the control in Bardonecchia station was legal under a 1990 bilateral agreement, but added they would be ready to clarify procedures with Italy to avoid further incidents.