The US agency FBI is sending seven bomb experts to Sweden to help investigate the weekend suicide attack claimed by an Islamist group, Sweden's intelligence agency said Monday.

The suicide bomber caused the twin blasts in a busy area of downtown Stockholm Saturday evening, in an attack probably meant to wreak carnage among Christmas shoppers.

"The FBI is sending a group of seven experts to Sweden," Saepo spokeswoman Sara Kvarnstroem told AFP. "From what I understand, they offered their help after Saturday's events and we said yes."

Islamic website Shumukh al-Islam named Taymour Abdelwahab as the attacker, saying he had "carried out the martyrdom operation in Stockholm."

A Swedish prosecutor said investigators were almost sure it was the same man.

In messages before the blasts, the bomber said he targeted Sweden over its military presence in Afghanistan and support of artist Lars Vilks, who drew the Prophet Mohammed with the body of a dog in 2007.

British and Norwegian authorities had also offered to help in the investigation, Swedish Justice Minister Beatrice Ask told the TT news agency.