Interior Minister Manuel Valls said in a statement that the suspect was arrested Wednesday morning in the Yvelines region just west of Paris, following the attack on Saturday that saw soldier Cedric Cordiez stabbed in the neck.

The attack on Saturday in a busy underground shopping and transport hub echoed the grisly killing of another soldier in London last week and authorities are seeking to determine if the Paris incident was a copycat.

A source close to the investigation said the suspect has been a follower of "traditionalist even radical Islam for the last three or four years."

"This is a young, recently converted Islamist who was already known to special police services for his religious convictions," another source close to the probe said.

But police sources urged caution in a case that is still in its early stages, saying the suspect was not previously known to authorities as a violent radical.

"The investigation will determine at what time he decided to carry out a jihadist act," one of the sources said.

The suspect was known to police for having carried out petty crimes and thefts, a source said.

Police said he was identified thanks to video footage from the crime and traces of his DNA found on items left at the scene in a plastic bag, including a knife and a bottle.

In his statement Valls said investigators were seeking to know more about the suspect's "motivation, background and family environment."

The Paris prosecutors' office was to hold a press conference on the arrest at 0930 GMT.

On French television, Valls warned of a growing number of young radicals in France similar to Mohamed Merah, the Islamist gunman who killed seven people in and around the southwestern city of Toulouse last year.

Valls said there are "several dozen, perhaps several hundred, potential Merahs in our country," saying young French Muslims were being "radicalised" on the Internet and by extremist imams.

The attacker, described by police at the time as bearded and around 1.9 metres (six feet three inches) tall, approached 23-year-old Cordiez while he was on patrol with two colleagues, stabbed him in the neck and then disappeared into a crowd.

Sources close to the investigation have said that the suspect was seen on video praying a few minutes prior to the attack.

Cordiez was released from a military hospital on Monday and rejoined his unit.