The announcement brought renewed pressure on the European Union from the U.S., Israel and Canada to designate the group a terrorist organization and to crack down on its fundraising operations across Europe. The EU, which regards Hezbollah as a legitimate political organization, has resisted such a move.

Interior Minister Tsvetan Tsvetanov said two of the suspects in the July 2012 attack had been living in Lebanon for years -- one with a Canadian passport and the other with an Australian one. He said investigators had traced their activities back to their home countries.

"We have well-grounded reasons to suggest that the two were members of the militant wing of Hezbollah," Tsvetanov said.

A third suspect entered Bulgaria with them on June 28, he said, without giving details.

Lebanese Prime Minister Najib Mikati condemned the attack and said his country would cooperate fully.

Hezbollah, a Shiite militant group and political party in Lebanon that emerged in response to Israel's 1982 invasion, has been linked to attacks and kidnappings on Israeli and Jewish interests around the world.

The group has denied involvement in the Bulgaria bombing, and Hezbollah officials in Beirut declined comment Tuesday.

The bomb exploded as the Israeli tourists were on their way from the airport to their hotel in the Black Sea resort of Burgas. The blast also killed a Bulgarian bus driver and the suspected bomber, a tall and lanky pale-skinned man wearing a baseball cap and dressed like a tourist.

Although it was initially believed to be a suicide bombing, Europol Director Rob Wainwright told The Associated Press that investigators now believe the bomber never intended to die. He said a Europol expert who analyzed a fragment of a circuit board determined that the bomb was detonated remotely. He said investigators were still looking into who detonated it and how one of the suspected bombers was killed.

Bulgarian investigators found no links to Iran, which Israel had accused of playing a role in the attack.

The findings increased pressure on Europe to declare Hezbollah a terrorist organization.

Israeli Prime Minister Benjamin Netanyahu called the investigation "further corroboration of what we have already known, that Hezbollah and its Iranian patrons are orchestrating a worldwide campaign of terror that is spanning countries and continents."

"We hope the Europeans learn the proper conclusions from this about the true character of Hezbollah," Netanyahu said.

The Obama administration called on Europe to take "proactive action" to disrupt Hezbollah.

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. "We need to send an unequivocal message to this terrorist group that it can no longer engage in despicable actions with impunity."

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."

U.S. officials also repeated the long-standing U.S. position that Washington wants the EU to designate Hezbollah a terrorist organization.

Canadian Foreign Affairs Minister John Baird echoed that call.

"We urge the European Union and all partners who have not already done so to list Hezbollah as a terrorist entity and prosecute terrorist acts committed by this inhumane organization to the fullest possible extent," he said.

France and Germany, wary of coming under pressure to condemn the group, had urged investigators not to publicly name Hezbollah in the bombing, according to a U.S. official who spoke on condition of anonymity because he was not authorized to speak to the news media.

Catherine Ashton, the European Union's top foreign policy and security official, said the EU would have to assess the implications of the investigation carefully.

Any decision on adding Hezbollah to the EU list of terrorist organizations would require a unanimous decision by the foreign ministers of all 27 EU countries, whose next scheduled meeting is Feb. 18. Under EU law, to declare a group a terrorist organization there must be proof that those who control it are terrorists, not just that its members were involved in a terror plot. The designation would also require the EU to freeze Hezbollah's assets in Europe and to work to choke off further funds reaching the group.

Wainwright -- whose organization helps coordinate national police across the EU, including in Bulgaria -- said that counterfeit U.S. driver's licenses found near the bombing scene were made in Lebanon. Tsvetanov said the fake licenses were from Michigan.

Wainwright said Bulgarian authorities found no direct links to Iran or to any al-Qaida-affiliated terror group.

"The Bulgarian authorities are making quite a strong assumption that this is the work of Hezbollah," Wainwright said. "From what I've seen of the case -- from the very strong, obvious links to Lebanon, from the modus operandi of the terrorist attack and from other intelligence that we see -- I think that is a reasonable assumption."

Despite its formidable weapons arsenal and political clout in Lebanon, Hezbollah's credibility and maneuvering space has been reduced in recent years, largely because of the war in neighboring Syria but also because of unprecedented challenges at home.

Hezbollah still suffers from the fallout of a monthlong 2006 war with Israel, in which it was blamed by many in the country for provoking an unnecessary conflict by kidnapping soldiers from the border area.

Since then, the group has come under increasing pressure at home to disarm, leading to sectarian tensions between Lebanese Shiite Hezbollah supporters and Sunni supporters from the opposing camp that have often spilled into deadly street fighting.

More recently, Hezbollah's support for the government of Syrian President Bashar Assad has proved costly to its reputation, and last week Israeli warplanes bombed what was believed to be a shipment of sophisticated anti-aircraft missiles headed to Hezbollah.

New troubles for Hezbollah could also add to Iran's international isolation. The Iranian regime is already under international sanctions for its suspect nuclear program, and has seen its position weaken due to its close ties with the Syrian regime. Its association with Hezbollah will likely further hurt Iran's international image.

Wainwright warned the attack is an indication of a real threat to Israelis and Jews in Europe.

"I don't want to exaggerate the scale of that threat, but I think law enforcement authorities -- government authorities -- should take notice of this incident and prepare for the possibility at least of similar attacks in Europe," he said.