British Prime Minister David Cameron met with his Bulgarian counterpart Boyko Borisov in London to discuss regional economic and security issues.
Cameron, in a statement issued through his spokesman's office, said "Britain stands ready to give Bulgaria every support in the investigation to bring the perpetrators to justice, and to respond robustly to the terrorist threat."
The leaders discussed ways to strengthen bilateral cooperation to deter organized crime and enhance their defense relationship.
A white male carrying a fake Michigan driver's license was identified as the likely suicide bomber who killed five Israeli tourists in the resort city of Burgas in late July.
Borisov had suggested the bomber likely had at least one accomplice. The operation was said to be sophisticated.
Israeli officials accused Iran and Hezbollah of coordinating the attack. Iran denied the allegations.