The Bulgarian government has blamed Lebanon’s militant Shiite Hezbollah organization for a deadly suicide bomb attack on a bus in the town of Burgas last July which left six people dead, five of them Israelis.

The long-awaited results of the Bulgarian investigation into the bombing will place greater pressure on the European Union to proscribe Hezbollah as a terrorist organization, a classification repeatedly called for by the US and Israel but so far rejected by the EU. European countries are concerned that proscribing Hezbollah could destabilize Lebanon, which is already reeling from the repercussions of the war in neighboring Syria, and potentially jeopardize European interests in the Middle East.

Tsvetan Tsvetanov, the Bulgarian interior minister, said that two suspects had been identified and that they had carried Canadian and Australian passports.

“We have well-grounded reasons to suggest that the two were members of the militant wing of Hezbollah,” he said after a meeting of Bulgaria’s national security council. “We expect the government of Lebanon to assist further in the investigation.”

However, the dominant player in the Lebanese government is Hezbollah, which will limit Lebanon’s ability to assist in the ongoing investigation.

Still, Najib Mikati, the Lebanese prime minister, repeated his condemnation of the Burgas bombing and said that Lebanon would cooperate with the Bulgarian authorities.

“[Lebanon] is keen on Bulgaria’s security and that of the EU states and on ensuring that these relationships will be maintained and developed on all levels,” he said in a statement.

There was no immediate reaction to the Bulgarian announcement from Hezbollah and the group’s spokesman was unavailable for comment.

Israeli Prime Minister Benjamin Netanyahu, who publicly blamed Hezbollah and its backer Iran for the bus bombing within hours of the July 18 attack, repeated his accusations that both were waging a “global campaign of terror” and urged the EU to blacklist the Lebanese party.

The White House also urged the EU to take "proactive action" against Hezbollah. John Brennan, the Obama administration's top counter-terrorism official, said the attack exposed Hezbollah as 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."

Rob Wainwright, the director of Europol, which helps coordinate national police forces in the EU, told the Associated Press that the bomb used in the attack was remotely detonated even though one of the bombers had died in the blast. He said that two counterfeit US drivers licenses found near the scene were traced back to Lebanon, where they were made.

“The Bulgarian authorities are making quite a strong assumption that this is the work of Hezbollah,” he 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 this is a reasonable assumption.”

European unease

To classify Hezbollah as a terrorist organization requires consensus among the 27 EU member states. While some countries, like Britain, already have placed Hezbollah on their national terrorism lists, many EU countries have expressed unease at blacklisting the powerful Hezbollah. Some, such as France, Italy, and Spain, have troops deployed with a United Nations peacekeeping force in south Lebanon which could make them vulnerable to reprisals. The peacekeepers have been targeted on several occasions in recent years by unclaimed roadside bomb attacks.

Additionally, some EU states worry that blacklisting an influential party like Hezbollah – which is politically powerful in government and parliament and runs an extensive social welfare network in addition to its militant activities – could destabilize Lebanon. That point was aired by Gilles de Kerchove, the EU’s top counter-terrorism official, in an interview last week with the online euobserver.com news portal.

“For Hezbollah, you might ask, given the situation in Lebanon, which is a highly fragile, highly fragmented country, is listing going to help you achieve what you want?... There is no automatic listing just because you have been behind a terrorist attack. It’s not only the legal requirement that you have to take into consideration, it’s also a political assessment of the context and timing,” he said.

In a statement, Catherine Ashton, the EU's foreign policy chief, said that the “implications of the investigation need to be assessed seriously as they relate to a terrorist attack on EU soil, which resulted in the killing and injury of innocent civilians.”

Hezbollah's international reach

Hezbollah was associated with a string of international bombing attacks against Western targets in the 1980s and early 1990s, but seemed to abandon global militancy in the late 1990s to concentrate on its domestic interests.

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However, in the past five years, Western intelligence agencies have noted a resumption of global activity by Hezbollah in association with the Quds Force, the external operations wing of the Iranian Revolutionary Guard Corps. The motives appear linked to the killing of Imad Mughniyah, Hezbollah’s top military commander who died in a car bomb explosion in Damascus in February 2008, and a series of assassinations against Iranian scientists and suspected acts of sabotage against Iran’s nuclear facilities.

In marked contrast to the bombing spectaculars attributed to Hezbollah in previous decades, the recent attacks generally have been poorly-planned, amateurish, and usually foiled before they could be carried out. The purported plots and attacks since 2008 spanned Thailand, Azerbaijan, Turkey, Kenya, and Cyprus. According to the New York police, there were nine thwarted international attacks alone planned by Hezbollah between January and July 2012.