"We confirm our urgent invitation (to Tehran) to sign without any preconditions" a UN protocol allowing unannounced inspections of its nuclear facilities, said Italian Foreign Minister Franco Frattini, whose country currently holds the EU's rotating presidency.
"The EU remains gravely concerned by Iran's failure to cooperate fully with the IAEA," added British Foreign Secretary Jack Straw, referring to the International Atomic Energy Agency (IAEA).
The EU comments came as IAEA head Mohamed ElBaradei prepares to begin a visit to Iran on Thursday, 15 days before a deadline expires for Iran to dispel suspicions it is pursuing a nuclear weapons programme.
Straw added that the EU will review its position depending on Tehran's actions in response to the October 31 deadline. "Iran's performance in this area will be critical if her relationship with the EU is to develop," he said.
In contast to the United States, the European Union is pressing ahead with a policy of constructive engagement with Iran, pressing it human rights issues at the same time seeking to negotiate a bilateral trade agreement.
But relations have been severely tested by the nuclear crisis.