Police arrest one, swoop on houses in cop killer investigation

French police on Tuesday arrested a man with suspected links to the killer of a police commander and raided several houses, the prosecutor's office said, part of a deepening investigation into last week's attack claimed by Islamic State.

The police probe is focusing on suspected associates of Larossi Abballa, the Frenchman of Moroccan origin who pledged allegiance to the Islamist militant group and told police negotiators during the attack that he had answered a call to "kill infidels at home with their families."

"There was a chance that these people might carry out other attacks against police officers. We were removing any doubt," said the Versailles prosecutor leading the investigation.

The prosecutor did not name the man who had been detained and it was not immediately clear whether police missed other targets or decided no further arrests were required.

Tuesday's swoop came after the Paris prosecutor's office said on Saturday that two other suspected associates were to be placed under investigation for membership of a terrorist organisation.

Abballa stabbed 42-year-old Jean-Baptiste Salvaing to death in a suburb west of Paris before taking Salvaing's partner, Jessica Schneider, and their son hostage. He used a knife to kill Schneider before he was shot dead by elite commandos.

Abballa was jailed in 2013 for his involvement in a militant recruitment network that sent young men to Pakistan. The men placed under investigation on Saturday, named as Charaf-Din Aberouz and Saad Rajraji, were founding members of the group and sentenced alongside Abballa, prosecutors said.

At this stage, investigators have not made any direct link between Aberouz and Rajraji and the killings last Monday, the first Islamic State-inspired attack in France since militant gunmen and bombers killed 130 people in Paris last November.