* Bulgaria wants EU solidarity over Burgas attack
* Says strong message crucial for EU security
* Sidesteps issue of blacklisting Hezbollah (Adds interview with Mladenov)
By Justyna Pawlak
BRUSSELS, Feb 18 (Reuters) - Bulgaria urged European governments on Monday to take a harder stance towards Hezbollah after blaming the Lebanese Islamist movement for a bus bombing that killed five Israelis at a Bulgarian Black Sea resort last year.
But the country's Foreign Minister Nikolai Mladenov cautioned European states not to be in a rush to brand the Lebanese group as a terrorist organisation, saying careful consideration was needed of potential consequences in Beirut.
Bulgaria's implication of Hezbollah in the attack in the city of Burgas has reignited a debate over Europe's approach to the Shi'ite Muslim group.
The European Union has resisted pressure from the United States and Israel to blacklist Hezbollah, arguing this could destabilise a fragile government in Lebanon and contribute to instability in the Middle East.
Hezbollah is a major player in Lebanese politics and its support is vital to the authority of Prime Minister Najib Mikati.
"It is very important for us in Europe to understand that when faced with the threat of terrorism, we need to stand up to it firmly ... and collectively," Mladenov told Reuters in Brussels, where he presented findings of an investigation into the July 2012 Burgas attack to EU foreign ministers.
On his way into the meeting, Mladenov told reporters Europe should take collective measures against Hezbollah.
Asked whether that meant the EU should blacklist the movement, he replied: "Given the fact that we've already made quite firm statements about where we believe the responsibility for that attack lies, I think the answer is quite obvious."
But he said it could take weeks or months before Bulgaria completes its investigation of the attack and shares all necessary information with other EU capitals to build the case for any moves against Hezbollah.
"I don't think we need to rush into this debate, before all the information we have is shared," he told Reuters.
Other European officials have said there are steps that could be taken short of blacklisting Hezbollah. These could include asking the EU policing agency Europol to coordinate investigations into the group's presence in Europe.
Mladenov said some governments wanted sanctions, such as travel bans and asset freezes, imposed on individual members of Hezbollah implicated in the Burgas attack. "We should look at the whole spectrum (of options)," he said.
Much will depend on evidence provided by Bulgaria linking Hezbollah to the attack, EU diplomats say.
Officials have said, for example, that France appears to have softened its traditionally staunch opposition to blacklisting the group, saying "all options" were on the table, provided the evidence is sufficiently strong.
The U.S. government said this month that Hezbollah must be held to account for the Bulgaria attack, and urged Europe and others to pursue an investigation into the incident.
But many European diplomats are wary that punishing Hezbollah would further radicalise the group and foment tensions.
"They see (Hezbollah) as a movement with a political and social base," said Julien Barnes-Dacey of the European Council on Foreign Relations.
"The fear is that sanctions...may push them into a position when it is no longer in their interest to hold back. It could isolate Hezbollah and therefore potentially empower the hardline elements." (Reporting by Justyna Pawlak; Editing by Michael Roddy)