Bulgarian police have released a computer-generated image of the suicide attacker involved in bombing in Bulgaria that killed five Israeli tourists and a Bulgarian bus driver two weeks ago.

A police statement said on Wednesday that the image of the dark-haired man was produced after reconstructing the badly damaged face of the bomber, who was decapitated in the explosion at a popular holiday resort on July 18.

The photo was sent to partner services for possible identification after fingerprints and DNA samples taken from the bomber did not match anything in international databases, said Interior Minister Tsvetan Tsvetanov.

He told reporters the explosives were attached to the bomber's back. 

Earlier reports had said that the bag of explosives was placed in the luggage compartment of a bus the tourists were travelling in at Burgas airport.

Investigators, who had found only the bomber's head and limbs, had also suggested the bomb had been attached to his torso.

Tsvetanov said the attacker had spent "at least 20 days in Bulgaria ahead of the bombing".

Last week, Prime Minister Boiko Borisov said a sophisticated group of conspirators was involved in the bombing at the Black Sea resort town.

Israel has blamed the attack on Iran and its proxy groups, including the Lebanese group Hezbollah. Iran and Hezbollah have both denied responsibility, and Bulgarian authorities have not blamed any particular group.