STRASBOURG, FRANCE (REUTERS) - A manhunt was under way in north-eastern France early on Wednesday (Dec 12) for a gunman who killed three people and wounded a dozen others at a Christmas market in the French city of Strasbourg on Tuesday evening.

France raised its security threat to the highest alert level, strengthened border controls and asked people around Strasbourg to stay put as and police searched for the suspect. German police also tightened border controls across the Rhine river, officials said.

Police identified the suspect as Strasbourg-born Cherif Chekatt, 29, who was known to the intelligence services as on the "S" watch list of suspected extremists.

"The hunt is continuing," Deputy Interior Minister Laurent Nunez said on France Inter radio. Asked whether the suspect might have left France, he said: "That cannot be ruled out."

Nunez said it was believed that the attacker had been injured by security forces but that could not be confirmed. His whereabouts now were unknown, and commandos and helicopters were involved in the manhunt.

A Reuters witness saw police briefly seal of an area near Strasbourg cathedral, but the operation ended quickly.

Nunez said the suspect had a police record and had been in jail several times, most recently at the end of 2015. He added the suspect had been monitored for religious radicalisation.

He also said police had searched the suspect's home early on Tuesday, before the attack, during a homicide investigation. He said five people have been questioned as part of that investigation.

Interior Minister Christophe Castaner said early on Wednesday that the shooter had evaded a police dragnet and was on the run, raising concerns of a follow-up attack.

"He fought twice with our security forces," Mr Castaner told a news conference held in the city. The attack also left 12 people injured, he said.

The Paris prosecutor said the motive for the attack was not known. No one immediately claimed responsibility, but the US-based Site intelligence group, which monitors jihadist websites, said Islamic State in Iraq and Syria (ISIS) supporters were celebrating.

The country remained on high alert after a wave of attacks commissioned or inspired by Islamic State in Iraq and Syria (ISIS) militants since early 2015.

People in the city's Neudorf area and Etoile park were told to stay where they were as officers hunted the shooter on the ground and from the air.

The European Parliament, which is sitting in Strasbourg this week, was put into lockdown.

"There were gunshots and people running everywhere," one local shopkeeper told BFM TV. "It lasted about 10 minutes."

The Christmas market was being held amid tight security this year, with unauthorised vehicles excluded from surrounding streets during opening hours and checkpoints set up on bridges and access points to search pedestrians' bags.

A source at the prosecutor's office said the motive for the shooting was not immediately clear.

A Reuters reporter was among 30 to 40 people being held in the basement of a supermarket for their own safety in central Strasbourg, waiting for police to clear the area. Lights were switched off and bottles of water handed out.

PRESIDENT INFORMED

President Emmanuel Macron was informed of the shooting and was being updated as events unfurled, an Elysee Palace official said.

A spokesman for the European Parliament said the building had been shut down and staff ordered to stay inside.

"My thoughts are with the victims of the Strasbourg shooting, which I condemn with the utmost firmness," tweeted Mr Jean-Claude Juncker, head of the European Commission.

"Strasbourg is an excellent symbol of peace and European Democracy. Values that we will always defend."

European security agencies have feared for some time that Islamist militants who left Europe to fight for ISIS would return after the extremist group's defeat, with the skills and motivation to carry out attacks at home.

In 2016, a truck ploughed into a Bastille Day crowd in Nice, killing more than 80 people, while in November 2015, coordinated Islamist militant attacks on the Bataclan concert hall and other sites in Paris claimed about 130 lives.

There have also been attacks in Paris on a policeman on the Champs-Elysees avenue, the offices of satirical weekly Charlie Hebdo and a kosher store.

And almost exactly two years ago, a Tunisian Islamist rammed a hijacked truck into a Christmas market in central Berlin, killing 11 people as well as the driver.