PARIS, April 20 (Reuters) - A French policeman was shot dead and two others were wounded in central Paris on Thursday night in an attack carrried out days before presidential elections and quickly claimed by the Islamic State group.

President Francois Hollande said he was convinced the shooting on the Champs Elyses boulevard, in which the assailant was himself shot dead by police, was an act of terrorism.

The wide avenue that leads away from the Arc de Triomphe had been crowded with Parisians and tourists enjoying a spring evening; but police quickly cleared the area which remained empty well into the night of all but heavily armed police and police vehicles.

The gunman, identified as Karim Cheurfi, had served time for armed assaults on law enforcement officers, police sources said on Friday, as authorities sought a second suspect flagged by Belgian security services.

Cheurfi, a French national who lived in the eastern Paris suburb of Chelles, had been convicted for previous armed assaults on law enforcement officers going back 16 years, the sources said, and was well known to authorities.