PARIS • French prosecutors yesterday requested preliminary terrorism charges against two suspected associates of the killer of a police commander and his partner, raising the spectre that the knife attack was part of a broader plot, the Wall Street Journal (WSJ) reported.

"Charaf-Din Aberouz and Saad Rajraji... will be brought before a magistrate as part of the judicial investigation in order to be placed under investigation for membership of a terrorist group," the prosecutor's office was quoted by Reuters as saying yesterday.

A decision on whether to file preliminary charges, which launches an official investigation, often closely follows such a referral, according to the WSJ.

The referral indicates that the authorities suspect Larossi Abballa, a 25-year-old Frenchman who killed the couple and took their three- year-old son hostage last Monday evening, was not acting alone.

Before he was gunned down by police, Abballa posted a video on Facebook warning there would be further attacks during the Euro 2016 soccer tournament.

The Islamic State in Iraq and Syria claimed responsibility for the assault.

Prosecutors said that the two arrested suspects had been convicted with Abballa in 2013 of being part of a French militant group that aimed to send fighters to join the Al-Qaeda in Pakistan and Afghanistan.

The duo had been sentenced to five years in prison, while Abballa had been sentenced to three years with six months suspended, according to WSJ.