TEHRAN, Iran - Iran said Thursday that foreign experts can accompany the international envoys Tehran has invited to inspect its nuclear facilities ahead of planned talks with world powers.

Foreign Ministry spokesman Ramin Mehmanparast said Iran's invitation to representatives of Russia, China, the EU, developing countries and Arab states to visit its nuclear facilities could be extended to the experts as well.

"There are no restrictions on bringing nuclear experts as companions," he said, in response to concerns by some country representatives that they didn't have sufficient expertise for the trip.

Mehmanparast said the invitation aimed at building trust ahead of talks Jan. 21 with world powers in Istanbul over Iran's disputed nuclear program, which the U.S. and many of its allies fear might be aimed at developing atomic weapons. Iran denies the charge, and says the program is peaceful.

Iran's offer pointedly did not include the United States, one of its biggest critics internationally, and many saw this as an attempt to divide the nations conducting the nuclear talks. Already a number of countries have indicated they may pass on the tour.

EU foreign policy chief Catherine Ashton already has said the EU would not take part in the trip and that the inspection of nuclear sites should be done by the U.N.'s International Atomic Energy Agency.

On Thursday, China also said it is unlikely to take up Iran's offer. Foreign Ministry spokesman Hong Lei said that "as our representative to Vienna is now at home, it will be difficult for him to visit Iran."

Russian Foreign Minister Sergey Lavrov, meanwhile, said that the invitation "deserves attention as any gesture showing some extra openness in relations with the international community," but maintained it could neither replace IAEA inspections or the upcoming Istanbul talks.

"The Iranian nuclear program is quite an acute problem now both because we aren't seeing due Iranian co-operation with the IAEA and also because excessive tensions are being fanned around it," Lavrov added.

Tehran said the sites to be visited include the uranium enrichment facility at Natanz and the Arak site where it is building a plutonium-producing heavy water reactor.

Both facilities are considered suspect by the West because they could be used to make the fissile core of nuclear warheads, and Tehran's refusal to shut them down has triggered U.N. Security Council sanctions.

Along with the U.S., Iran's offer also snubbed three European countries that have been more critical of Iran -- Britain, France and Germany. Those four countries, however, will take part in the Istanbul talks, along with Russia and China.

Iran's IAEA envoy Ali Asghar Soltanieh also said the representatives from Egypt, Algeria, Venezuela and Syria would visit the sites on Saturday and Sunday, according to IRNA, the state news agency.