French police arrest four over Lyon package bomb blast

French police arrested four people Monday over a package bomb explosion in the heart of the southeastern city of Lyon last week which injured 13 people, authorities said.

A police raid was under way in a building in the Oullins suburb just south of the city, a few hours after the arrest of the suspected bomber, a 24-year-old Algerian IT student.

The man's parents were later arrested and taken in for questioning, as was a second student of Algerian nationality who is a family relation, according to the Paris prosecutor's office, which has jurisdiction over terrorism cases in France.

The suspect was previously unknown to police, Lyon's Mayor Gerard Collomb said. Interior Minister Christophe Castaner told a press briefing in Lyon that he had no further details on the suspect.

"Nothing has been established at this point," he said. "I ask you to let the investigation take its course." The youth was arrested as he got off a bus, calmly putting his hands in the air when he spotted officers approaching, Collomb said.

The man's sister has also been questioned but she has not been arrested, prosecutors added.

Police had been searching for a man seen cycling near the scene of the blast wearing a green top and Bermuda shorts and carrying a dark-coloured rucksack.

He has been the target of an extensive manhunt since late Friday when an explosive device filled with screws and ball bearings was placed in front of a bakery near the corner of two crowded pedestrian streets in the historic centre of Lyon.

Police circulated photos of the suspect on Twitter, which they said led to "several dozen" calls from people with information.

Sources close to the investigation said the explosive was most likely acetone peroxide, or APEX, a volatile compound used in the deadly Paris terror attacks of November 13, 2015.

Investigators recovered small screws, ball bearings and batteries along with a printed circuit board and a remote-controlled trigger device. Officials later said the charge was relatively weak.

Thirteen people were wounded in the blast -- eight women, four men and a 10-year-old girl -- of whom 11 needed hospital treatment.

None of their injuries are believed to be life-threatening, though authorities said some needed surgery to remove shrapnel.

France has been on high alert following a wave of deadly jihadist terror attacks since 2015 which have killed more than 250 people.

The Islamic State group has been behind many of the attacks. No one has claimed responsibility for the Lyon blast.