US President Barack Obama pledged solidarity with Bulgaria, two days after a "barbaric attack" by a suicide on a bus of Israeli holiday-makers left six people dead.
In a telephone call with Bulgarian Prime Minister Boyko Borissov, Obama "offered his support for the ongoing investigation, and for the Bulgarian people in this challenging time," the White House said in a statement.
The two leaders discussed the "strong partnership and excellent counterterrorism cooperation" their countries share, it added, saying Obama "reiterated his condemnation of the barbaric attack."
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The FBI and the CIA are working together with Bulgarian investigators to try to identify the people behind Wednesday's the suicide bombing.
The attack, the first of its kind in Bulgaria, killed five Israelis and their Bulgarian bus driver. The bomber, who struck as the bus was making its way from the Burgas airport to resorts on the Black Sea, also died.
Airport video footage released by Bulgarian authorities of the suspected bomber showed an apparently white male in his mid-thirties with long hair, possibly a wig, carrying a backpack and a laptop bag.
Israel has blamed Iran and its "terrorist proxy" Hezbollah for the attack, charges they both vehemently deny.
In the aftermath of the attack, Obama phoned Israeli Prime Minister Benjamin Netanyahu to offer his condolences and support.
