The man, named Nordine Amrani, aged 33, also threw grenades into a crowded square from a rooftop before killing himself.

Amrani was known to police for firearms offences. He was jailed for 58 months in September 2008 for possessing firearms and drugs, media reports said.

Two of the people confirmed dead were boys aged 15 and 17, the third a 75-year-old woman.

A city hospital also announced the death of a fourth victim, a 17-month-old girl.

Medical staff at a field hospital at the scene treated 52 of the injured. Some others made their own way to other hospitals.

Belgian Prime Minister Elio di Rupo, visiting the scene, described the attack as "horrible". "There are no words to describe this tragedy," he said.

Belgium's King Albert and Queen Paola also came to pay their respects.

Place Saint-Lambert is a busy intersection, served by hundreds of buses daily. It hosts an annual Christmas market which attracts some 1.5 million visitors a year.