Police beefed up their presence in Stockholm Tuesday as investigators hunted for possible accomplices of a suicide bomber who narrowly missed wreaking carnage among Christmas shoppers at the weekend.

"The threat level has not been raised, but after what happened, we think Stockholm residents need to see more police around town, to talk to us about this very serious event that has taken place," Stockholm police spokesman Kjell Lindgren told AFP.

"We have an additional force of around 40 police officers, in addition to volunteers, who are out on the street, in the subways, train stations, shopping centres and everywhere it is crowded to make our presence felt," he added.

A man strongly believed to have been Taymour Abdelwahab was the only person to die Saturday when he first blew up his car and shortly after himself near a crowded pedestrian street in central Stockholm.

Two other people were injured by the car blast.

He was carrying a cocktail of explosives, and is believed to have mistakenly set off a small explosion that killed him before he could carry out what appears to have been a mission to kill "as many people as possible," Sweden's chief prosecutor for security cases, Tomas Lindstrand, said Monday.

Sweden's intelligence agency Saepo meanwhile said it had launched "a broad international cooperation" with authorities "in the other Nordic countries, the rest of Europe and of course in the United States" in their search for possible accomplices of the bomber.

"We are looking into different kinds of leads," Saepo spokeswoman Sofia Oliv told AFP Tuesday, without giving details.

Oliv refused to comment on work mapping Islamic extremists within Sweden, but according to the Aftonbladet daily, a yet unpublished report from the intelligence agency shows it knows of around 200 such people living in the Scandinavian country.

According to the paper, up to 80 percent of these people were part of so-called "violence-prone networks," while the remainder were "loners" and people with extremist contacts abroad.

Seven bomb experts from the US Federal Bureau of Investigation were according to Saepo on their way to Sweden to help with the investigation, which is being conducted in close cooperation with British police, since Abdelwahab lived in the British town of Luton with his wife and three children.

The chairman of a mosque in Luton where the suspected bomber used to worship described him as a "bubbly" character who had been known for his hardline views before he "stormed out" for good when tackled about them in 2007.

"I had to confront him three or four times because his views were so extreme," Qadeer Baksh told AFP.

"He was saying physical jihad was an obligation for all Muslims," Qadeer Baksh told AFP.

Foreign Minister Carl Bildt told the BBC late Monday the bomber appeared to have been "heading into probably the most crowded place of Stockholm at the most crowded time of the year.

"He was heading into a place where if he had exploded all of the ordnance that he had with him... it would have been mass casualties of a sort that we have not seen in Europe for quite some time."

He added: "We were extremely lucky... I mean minutes and just a couple of hundred metres from where it would have been very catastrophic."

Prosecutor Lindstrand sketched a similar scenario to reporters: "He had a bomb belt on him, he had a backpack with a bomb and he was carrying an object that has been compared to a pressure cooker.

"If it had all blown up at the same time, it would have been very powerful," he said.

Abdelwahab would have been 29 the day after the blasts.

He was reportedly born in Iraq, but investigators said he became a Swedish citizen 18 years ago. He had never come to the attention of the security services, they added.

An Islamist website, Shumukh al-Islam, posted a purported will by Abdelwahab which said he was fulfilling a threat by Al-Qaeda in Iraq to attack Sweden.

On Saturday, Saepo and the TT news agency received an email with audio files in which a man believed to be the bomber is heard calling on "all hidden mujahedeen in Europe, and especially in Sweden, it is now the time to fight back."