US officials say the suicide bomber who targeted Israeli tourists in Bulgaria this week was part of a Hezbollah cell, the New York Times reported, after Israel made similar allegations.
The Times on Thursday cited two US officials as saying that Hezbollah was behind the attack, which killed six people, including five Israeli tourists.
It cited a third official as saying that the bomber was "acting under broad guidance" from the Lebanese Hezbollah group and its main sponsor Iran to strike Israeli targets of opportunity.
Israeli officials have publicly accused Iran and Hezbollah of carrying out the attack, though observers say it is unlikely to take military action against either Iran or Lebanon in response to it.
The bombing on Wednesday of a bus at Burgas airport on the Black Sea killed five Israeli tourists and injured more than 30, Israel's foreign ministry said, in what was the deadliest attack on Israelis abroad since 2004.
US President Barack Obama condemned the "barbaric terrorist attack" shortly after it happened on Wednesday but did not mention Iran in his statement.
The attack came on the anniversary of an attack on a Jewish community center in Buenos Aires in 1994 that killed 85 people and wounded 300. That attack was also blamed on Iran, which denied the charge.
Iran said Thursday it condemns "all terrorist acts in the world" and dismissed Israeli allegations of responsibility for the Bulgaria bombing.