Hezbollah is behind an attack on a bus filled with Israeli tourists in Bulgaria last year, investigators said Tuesday, describing a sophisticated bombing carried out by a terrorist cell that included Canadian and Australian citizens.

In the first major announcement in the investigation into the July 18 bombing that killed five Israelis and their Bulgarian driver, Interior Minister Tsvetan Tsvetanov said one of the suspects entered the country with a Canadian passport, and another with one from Australia.

"We have well-grounded reasons to suggest that the two were members of the militant wing of Hezbollah," Tsvetanov said after a meeting of Bulgaria's National Security Council. "We expect the government of Lebanon to assist in the further investigation."

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

Hezbollah, a Shiite militant group and political party that emerged in response to Israel's 1982 invasion of Lebanon, 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 further comment Tuesday. Hezbollah officials as a rule leave it to their leader, Sheikh Hassan Nasrallah, to comment on security issues.

The bomb exploded as the bus took a group of Israeli tourists from the airport to their hotel in the Black Sea resort of Burgas. The blast also killed 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 recovered from the scene determined that it was detonated remotely.

The 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 to be a terrorist organization, as the United States and Canada do.

"The attack in Burgas was an attack on European land against a member of the European Union," Israeli Prime Minister Benjamin Netanyahu said. "We hope the Europeans learn the proper conclusions from this about the true character of Hezbollah."

The White House called on Europe to take "proactive action" to disrupt Hezbollah. Counterterrorism adviser John Brennan, who is President Barack Obama's nominee to run the Central Intelligence Agency, said Europe and other international partners should seek to uncover Hezbollah's infrastructure and disrupt the group's finances and operational network.

Canadian Foreign Affairs Minister John Baird went further.

"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, adding that Canada would work with Bulgarian authorities given the apparent involvement of "a dual national living in Lebanon."

Catherine Ashton, the European Union's high representative for foreign and security policy, said the EU needs to assess the implications of the investigation seriously but stressed that any decision on adding Hezbollah to the EU list of terrorist organizations would require a unanimous decision by the foreign ministers of the 27 EU countries, whose next scheduled meeting is Feb. 18. Such a move would freeze Hezbollah assets and cut off funding.

France and Germany, wary of coming under increased pressure to do so, had pressured investigators not to publicly name Hezbollah as responsible for 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.

The investigators' reports offered the first glimpse at how the bombing was carried out.

Wainwright -- whose organization helps coordinate national police across the EU, which includes Bulgaria -- said in an interview that two counterfeit U.S. driver's licenses that were found near the bombing scene were made in Lebanon. The investigators, he said, found no direct links to Iran or to any Al Qaeda-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."

For Hezbollah, the accusation comes at a horrible time.

Despite its formidable weapons arsenal and political clout in Lebanon, the group's credibility and maneuvering space has been significantly 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 month-long 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, along with a wave of attacks against Israelis around the world in the past year, is an indication of a real threat to Israelis and Jews in Europe.

"Even if it's not Hezbollah, it has still obviously been carried out by an organization with some capability in the world, so the threat remains," Wainwright said. "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."