EU foreign affairs chief Catherine Ashton says the European Union welcomes Iran's invitation to visit its nuclear facilities but that the task should be carried out by the International Atomic Energy Agency (IAEA).
Ashton told the Reuters news agency that she had consulted with Russia and China before taking the decision that the invitation should be turned down.
She was speaking in Budapest on the sidelines of a meeting with Hungarian Foreign Minister Janos Martonyi.
In Brussels, Ashton spokeswoman Maja Kocijancic confirmed the EU's stance on the issue.
"We believe that the inspectors of the IAEA, the International Atomic Energy Agency, are best placed to view different nuclear facilities in Iran and the high representative [Catherine Ashton] has reaffirmed this position," Kocijancic said.
Iran has invited some diplomats accredited to the IAEA to visit nuclear facilities in the Islamic Republic.
The invitation comes ahead of a new round of talks over Tehran's controversial nuclear program, which the West suspects is aimed at developing bombs.
Some Western diplomats see Iran's overture as an attempt to split the six powers involved in talks with Iran.
Iran invited Russia and China but not the other four countries involved in the nuclear talks -- Britain, France, Germany, and the United States.
compiled from agency reports