The lone gunman armed with grenades who went on a murderous spree in the Belgian city of Liege shot himself in the head after slaying three youngsters on a crowded square and killing a woman, the prosecutor said on Wednesday.

A man displays a Christmas ball amid flowers and candles gathered in a broken bus shelter, one of the targets of the Tuesday shooting on the Place Saint-Lambert in Liege on Wednesday. The gunman who went on a murderous spree in the Belgian city of Liege shot himself in the head after slaying three youngsters on a crowded square and killing a woman, the prosecutor said. [China Daily via Agencies]

"Nordine Amrani committed suicide with a bullet to the head," Daniele Reynders said at a news conference. "He left no message to explain his act."

The statement cleared up speculation that the 33-year-old with a long criminal record may have died when a fourth grenade he was carrying exploded accidentally.

In all, police found nine magazines in his bag along with his automatic rifle, hand-gun and several grenades, Reynders said.

Two youngsters ages 15 and 17 and a baby of 17 months died in Amrani's lunch-hour grenade and gun attack on Liege's central square, packed with Christmas shoppers and children just out of school.

The baby was the latest victim after succumbing to injuries overnight, with a 75-year-old woman previously reported dead said by the prosecutor to be alive but in critical condition, along with several others.

Around 120 people were injured, said Home Affairs Minister Joelle Milquet, who broke off European Union talks to dash to Liege along with King Albert II and Queen Paola, and Belgium's just-named Prime Minister Elio Di Rupo.

"The entire country feels the pain," Di Rupo said.

Earlier on Wednesday, police also discovered the body of a dead cleaning woman around the age of 40 lying in a shed used by Amrani to stash cannabis plants and illegal weapons.

Released on parole just over a year ago for drug offenses, Amrani had been summoned by police in the morning but never showed up.

"He liked arms and had a record, but he was a very poised, very calm man," said one of his former lawyers - who goes by the same surname but is not related - Abdelhadi Amrani.

"I would never have expected him to be behind the drama in Liege," he told RTBF television. "He must have snapped."

Amrani, who in 2003 was convicted for vice but given a suspended sentence, was released from jail on parole in October 2010 after serving much of a 42-month drugs sentence delivered when he was arrested in possession of 2,800 cannabis plants in 2007.

The prosecutor would not say exactly why he had been summoned by police, saying simply that since his parole the summons "in a vice inquiry" was his only brush with police.

The vice squad "was interested in him due to a license-plate" linked to a complaint they were investigating.

The daily Le Soir said the investigation was over sexual harassment.

Instead of heading to the police station, Amrani drove to the central Saint Lambert Square, climbed onto the roof of a bakery and lobbed grenades into packed bus shelters before opening fire on the panicked crowd, according to witnesses.