The European Union will be taking its time before blacklisting the Lebanese Islamist group Hezbollah, the European Commission said on Thursday.

"The European Union won't make a decision on whether to blacklist Hezbollah as a terrorist movement until an investigation into a bus bombing in Burgas has wrapped and the perpetrators have been prosecuted," European Commission chief, Jos? Manuel Barroso said after a meeting with Israeli President Shimon Peres.

The investigation and subsequent trial "will show if we have to take political steps, but we can't decide before that," according to Barroso.

"Blacklisting an organisation as a terrorist movement takes careful consideration given the legal, political and security implications".

"Member states need to agree unanimously, it's not down to the European Commission," he added.

"Of course we are extremely concerned and we condemn in the strongest terms the attack on Israeli tourists in Bulgaria. As you know on February 5th Bulgaria announced the preliminary findings of the investigation into the attack at Burgas.

Bulgaria has asked for more help from Lebanon in the investigations and now things need to take their course. The investigative and judicial processes will show if we have to make any decisions, but we can't do anything before that".

Barroso wrapped things up by saying: "The immediate goal is to bring the perpetrators of those terrorist attacks to justice.

There can be no impunity. Once we know who is guilty we can update the list of terrorist organizations and apply specific measures to combat terrorism."

Bulgaria in February implicated Hezbollah in a bombing in the Black Sea resort of Burgas last year that killed five Israelis, putting pressure on the EU to sanction the group.

Israel also has stepped up lobbying in Brussels and Paris, calling on European governments to follow the United States in listing the Shi'ite Muslim group as a "terrorist organization" and impose financial sanctions on it.

Many European governments are cautious, arguing that imposing sanctions on Hezbollah could destabilize the government in Beirut and contribute to tensions in the Middle East.

Hezbollah is a dominant force in Lebanese politics, with Prime Minister Najib Mikati relying on the group for support.