The European Union on Wednesday said in reply to Tehran's invitation to several nations to tour its nuclear sites that it was up to the International Atomic Energy Agency (IAEA) to carry out the visits.

A spokesman for the EU's foreign policy chief Catherine Ashton said the 27-nation bloc had received a letter of invitation to visit the sites.

"There is a process going on," said Michael Mann. "It is for the IAEA to visit."

Iran's foreign ministry said Tuesday that invitations to visit Iran's nuclear sites in Natanz and Arak have been sent to ambassadors of some of the nations represented in the IAEA.

Diplomatic sources at the Vienna-based nuclear watchdog said invitations had gone out to Russia, China, Egypt and Cuba as well as to Hungary as rotating president of the European Union.

The EU spokesman said the bloc had not answered the letter and reiterated that the IAEA "are the people who have to inspect the Iranian nuclear facilities."

The unusual move comes in the run-up to talks between Iran and six world powers in Turkey at the end of January chaired by Ashton.

Britain, China, France, Russia, the United States and Germany are to meet with Iran for another round of talks on Tehran's atomic programme. The previous round of talks, after a 14-month hiatus, was held in Geneva on December 6-7.

"We are looking forward to the talks," Mann said.

IAEA sources said Britain, France, Germany and the United States were not on the list of countries invited to see the sites.