The EU also warned on the final day of a two-day summit in Brussels that any wider cooperation with Iran hinged on the Islamic republic reassuring the world that it was not building nuclear weapons.
"The European Council renews its call on Iran promptly and unconditionally to sign, to ratify and to implement" an additional protocol to the nuclear Non-Proliferation Treaty that would allow unscheduled checks by international inspectors.
"It also calls on Iran to suspend all uranium enrichment-related and reprocessing activities," it added.
The UN's nuclear watchdog body, the International Atomic Energy Agency, has set an October 31 deadline for Iran to prove it is not developing nuclear weapons as feared by its arch-enemies the United States and Israel.
"The European Union remains ready to explore ways to develop a wider cooperation with Iran," the EU's final statement said.
"This can only be achieved through increased international confidence on the peaceful nature of Iran's nuclear programme and improvements in the areas of human rights, fight against terrorism and Iran's position on the Middle East."
At an Islamic summit in Malaysia, Iran's President Mohammad Khatami said Friday his country "excluded" the building of a nuclear bomb and that it was continuing to cooperate with the IAEA.
IAEA chief Mohamed ElBaradei, on a flying visit to Iran, said Thursday that he had received assurances of Iran's "readiness" to open up its suspect facilities but that Tehran had still not agreed to stop enriching uranium.
EU leaders also congratulated Iran's new Nobel Peace Prize winner Shirin Ebadi "in recognition of her commitment to democracy and the defence of human rights in Iran," he said.