Three people were killed and more than 20 injured on Wednesday in a blast on a bus at Bulgaria's Black Sea airport, the interior ministry said, with reports saying the vehicle had Israelis on board.

"Three people were killed and over 20 injured," an interior ministry press officer told AFP, adding that "their nationality is yet to be determined."

An explosion rocked one Israeli-packed bus at the Black Sea airport, state BNR radio reported, adding that two more buses also caught fire.