Iran has condemned the European Union's decision to put the armed wing of Lebanese militant group Hezbollah on its terrorism blacklist.
It said the move was "contrary to all political and legal norms, surprising and unacceptable".
Hezbollah was set up with the help of Iranian funds and military advisers three decades ago.
Along with Syria, it is Iran's most important ally in the region.
Pressed by Britain and the Netherlands, the EU blacklisted Hezbollah's military wing yesterday over accusations it was involved in a bus bombing in Bulgaria that killed five Israelis and their driver a year ago, and its deployment of thousands of fighters to help Syrian President Bashar al-Assad turn the tide of Syria's civil war.
Many EU governments had previously resisted lobbying from the US and Israel to blacklist the group.
They warned such a move could fuel instability in the Middle East, especially in Lebanon, where Hezbollah is part of the Lebanese government and has dominated politics in Beirut in recent years.
"To label a resistance group which has campaigned against invasion and occupation and has a legal presence with the people's support in the government of Lebanon shows it is based on loose logical foundations," Iranian Foreign Minister Ali Akbar Salehi said in a statement on the ministry website.
"This action was accomplished with the direction of some influential members of the European Union and is contrary to all political and legal norms, surprising and unacceptable," he said.
Israel, which welcomed the EU decision, would be the main beneficiary, the Iranian foreign minister said.
"This action will be to the benefit of the illegitimate Zionist regime and its supporters."