French police investigating Sunday's knife attack that left two young women dead in the southern port of Marseille said they detained four people Tuesday.
A judicial official said the four were in custody on suspicion of association with a terrorist group. Several places were being searched in the probe.
The official, who spoke on condition of anonymity under internal rules, wouldn't give more details.
Interior Minister Gerard Collomb said on France-Inter radio Tuesday that the assailant in Sunday's attack had Italian residency and a valid Tunisian passport. The attacker was killed by soldiers after the stabbings, which were claimed by the Islamic State group.
One of the seven IDs the attacker used in previous encounters with French police was a Tunisian passport identifying him as Ahmed H. A judicial official said Tuesday that authorities have determined that is the Marseille attacker's true identity.
Rome prosecutors opened a terrorism investigation into the suspect, identified in the Italian media as Ahmed Hanachi. He had lived in Aprilia, south of Rome, from about 2006 to 2014, Italian news agency ANSA said.
According to Paris Prosecutor Francois Molins, he didn't have any past convictions in France. Hanachi's most recent arrest occurred in the Lyon area Friday—just two days before the train station stabbing. He was detained on suspicion of shoplifting and released the day before the attack.
Hanachi also had a record for petty crimes but no terrorism-related offenses or indications he had been radicalized, Italian daily La Repubblica said.
The reports said he lived in an area with a sizeable Tunisian community, and had married then divorced an Italian woman.
The region has already seen four people expelled from Italy for alleged radicalization-related reasons, Repubblica said.
Citing state security, Italy has expelled more than 200 people since 2015 who are suspected of radicalizing others or recruiting would-be jihadis—offenses that wouldn't necessarily hold up in court but which the Interior Ministry uses as reason to expel them.
The area south of Rome was also where the Berlin Christmas market attacker, Anis Amri, spent about a week in July 2015 after getting out of an Italian prison. There's no indication the two ever crossed paths, Repubblica said, without citing sources.