An explosion has killed at least four people on a bus carrying Israeli tourists in the eastern Bulgarian city of Burgas, BBC News reported.


More than 20 people were also injured when the bus exploded at Burgas airport, by the Black Sea.


Witnesses have told Israeli TV that someone boarded the bus and a huge explosion immediately followed.


Israeli Prime Minister Benjamin Netanyahu later accused Iran of being behind the explosion.


"All the signs lead to Iran," he said in a statement. "Israel will respond forcefully to Iranian terror."


Iran has made no public comments to the Israeli accusations.


Wednesday's blast came on the 18th anniversary of a deadly attack on a Jewish community centre in Argentina. Israel blamed Iran for that attack - a claim denied by Tehran.