Three more suspects have been placed under formal investigation over the killing in April of a Paris police officer in an attack claimed by Islamic State, a judicial source said on Sunday.

Officer Xavier Jugele died on April 20 after being fired on by Karim Cheurfi, 39, on the French capital's Champs Elysees shopping street. Cheurfi was immediately shot dead by the policeman's colleagues.

The three suspects, identified as Nourredine A., Mohamed D. and Yanis A., were remanded in custody on charges of associating with terrorists, the judicial source said.

Nourredine A., who is believed to have supplied the assault rifle used in the crime, is also accused of conspiracy to murder a law enforcement official and weapons offences.

A first suspected accomplice was placed in detention last month on charges of associating with terrorists and carrying an illegal weapon for terrorist purposes.