The mayor of the city, on Bulgaria's Black Sea coast, said the bus was carrying Israeli tourists, but police could not immediately confirm their nationality. Police said several other buses at the site had been damaged.

"Initial information showed three people have died, there are injured," a spokeswoman for the interior ministry said.

An Israeli witness said in an interview with Israeli army radio that the explosion was probably caused by a suicide bomber at the entrance of the bus.

Bulgarian police said it was investigating and could not say at this point what caused the explosion.

Bulgarian national radio said many people were injured in the blast. Burgas airport was closed after the incident and flights were redirected to the airport of Varna, police said.

Israeli officials had previously said that Bulgaria, a popular holiday destination for Israeli tourists, was vulnerable to attack by Islamist militants who could infiltrate via nearby Turkey.

(Reporting by Tsvetelia Tsolova; editing by Ralph Boulton; Editing by Louise Ireland)

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