BRUSSELS (AFP) - Ending months of hesitation, the European Union opened the door on Tuesday to adding the military wing of Lebanon's Hizbollah to its list of international terrorist groups, EU diplomats told AFP.

A formal request to blacklist Lebanon's most powerful political and military group was filed by Britain and is to be discussed at closed-door talks June 4 of a committee overseeing the EU list of people and groups subject to its asset freezing regime.

"We hope to have an agreement by the end of June on Hizbollah," said a diplomat close to the matter who spoke on condition of anonymity.

A decision to add the Shi'ite militia to the dozen people and score of groups currently blacklisted by the EU - including Hamas and Colombia's FARC guerrillas - will require unanimity from the 27 EU states.

Despite months of strong and steady pressure from Israel and the United States to follow their example and designate Hizbollah as a terrorist group, the EU has up until now skirted an issue seen as sensitive and divisive, with Britain openly in favour but France and Italy reluctant.

As the former colonial power, France fears destabilising politically fragile Lebanon, where Hizbollah is the leading political group and part of the government, while heading a militia more powerful than the country's army.

There was concern too from France, Italy and Spain for the safety of national troops committed to the UN peacekeeping force, UNIFIL.

Italy is a major contributor, making it sensitive to the risk of reprisals, but its position is also based on a view of Hizbollah as a legitimate political force, not merely a military organisation.

The United States said on Tuesday it does not differentiate between Hezbollah's armed and political wings as it again urged Europe to blacklist the group.

State Department spokesman Patrick Ventrell told AFP the US was "increasingly concerned about Hizbollah's activities on a number of fronts - including its stepped up terrorist campaign around the world, and their critical and ongoing support" for Bashar al-Assad's regime in Syria.

Asked just how the EU would differentiate in applying sanctions between members of Hizbollah's military wing and its political leadership, an EU official said "we cannot comment on such detail." But mounting global concern over the Shi'ite group's active support of Assad has finally swayed even the most reluctant EU nations into shifting gear.

"Hizbollah's role in Syria convinced member states it was time to act," one diplomat said.

As Hizbollah fighters joined a Syrian government assault on the rebel bastion of Qusayr, President Barack Obama on Monday "stressed his concern about Hizbollah's active and growing role in Syria, fighting on behalf of the Assad regime which is counter to the Lebanese government's policies."

In Europe, the mood shifted last year after an attack on Israeli tourists in Bulgaria which Sofia blamed on Hizbollah. In March, a Cyprus court sentenced a Hizbollah member to four years behind bars for planning attacks there.

During a visit to Brussels in March, Israeli President Shimon Peres urged the EU to put Hizbollah on the terrorist list, saying it was behind a score of attempted attacks in Europe and arguing that its intervention in Syria against anti-Assad rebels was enabling the group to spread its reach.

"If you do not take measures against Hizbollah, then they may think that they are permitted" to do what they like, Mr Peres said after meeting European Commission head Jose Manuel Barroso.

Hizbollah has been on a US terror blacklist since 1995 after a series of anti-American attacks, including the bombing of the US embassy and Marine barracks in Beirut in the 1980s.

US Secretary of State John Kerry has urged the EU to follow Washington's lead in a move that will notably lead to a crackdown on the group's fund-raising activities.

Currently, Britain and the Netherlands are the only EU nations to have placed Hizbollah on their lists of terrorist groups.