This looks like it will lead to a few more people involved.

The attacker allegedly spent time with the woman at a three-star hotel in the Black Sea resort of Varna before travelling to Burgas to carry out his attack, sources in the Bulgarian newspaper Troud claimed.

Along with hunting for the mysterious woman, Bulgarian police are also looking for one more accomplice. According to sources quoted by local media, investigators believe the bomber had two companions with him on the day of the attack, one of whom coordinated the operation while the other acted in support.

A taxi driver claims to have driven the bomber from Ravda to Pomorie two small towns north of Burgas in the early hours of July 18, the day of the attack, and that he spoke “decent Russian”.

The latest details add to the mystery over just who the attacker was and what group organised the bloody blast. Israel has insisted that the Lebanese group Hizbollah, acting on the behest of Iran, orchestrated the operation but so far no organisation has claimed responsibility, and there is no conclusive evidence linking Hizbollah to any other bomb attacks outside the Middle East.

But the newspaper Novinar said that the police are hunting a Hizbollah cell in the country’s Pirin Mountains, and are exploring the possibility that the Lebanese group made contact with local sympathisers.