WASHINGTON (AP) — The Obama administration called Tuesday for Europe to take "proactive action" to disrupt the Hezbollah organization following an investigation that tied the group to the deadly bombing of a bus filled with Israeli tourists in Bulgaria last year.

In strongly worded statements, Secretary of State John Kerry and White House counterterrorism adviser John Brennan said the Europeans, along with other countries that have balked at imposing sanctions on Hezbollah, must act to prevent additional attacks.

"We strongly urge other governments around the world - and particularly our partners in Europe - to take immediate action to crack down on Hezbollah," Kerry said in his first substantive statement as secretary of state. "We need to send an unequivocal message to this terrorist group that it can no longer engage in despicable actions with impunity."

Kerry also discussed the matter with European Union foreign policy chief Catherine Ashton in a phone call, the State Department said.

In his statement, Brennan, who is President Barack Obama's nominee to run the Central Intelligence Agency, said the Bulgarian investigation "exposes Hezbollah for what it is: a terrorist group that is willing to recklessly attack innocent men, women, and children, and that poses a real and growing threat not only to Europe, but to the rest of the world."

"We commend Bulgarian authorities for their determination and commitment to ensuring that Hezbollah is held to account for this act of terror on European soil," he said.

Earlier Tuesday in Sofia, investigators implicated Hezbollah in last July's bombing, which killed five Israelis and their Bulgarian driver. The findings are expected to put pressure on the European Union to designate Hezbollah as a terrorist organization, as the United States and Israel have done. Some European countries are opposed to making such a designation because Hezbollah also operates as a legal political party in Lebanon.

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AP White House Correspondent Julie Pace contributed to this report.