The diplomats, among them representatives of some member states of the UN atomic watchdog, the International Atomic Energy Agency (IAEA), visited the heavy water facility at Arak on Saturday.

On Sunday, they are to tour Iran’s main uranium enrichment facility in the central city of Natanz where the material is being refined despite objections by the West.

Iran’s atomic chief and acting foreign minister Ali Akbar Salehi said Saturday Iran will push ahead with the enrichment work *”very strongly,”* dismissing reports that sanctions and technical problems have hampered the nuclear drive.

*”The recent sanctions did not create any problems for our nuclear activities,”* Salehi told a news conference in Arak broadcast live on state television.

*”Our nuclear activities are going forward strongly. Our activities, especially in (uranium) enrichment, are also continuing very strongly … The production of enriched uranium is growing.”*

World powers, led by Washington, want Tehran to stop the uranium enrichment, which they suspect is aimed at making weapons. Iran says it nuclear activities are entirely for peaceful purposes.

The dispute will be at the centre of talks between Tehran and six world powers — Britain, China, France, Russia, the United States and Germany — in Istanbul on January 21 and 22.

Iran at the end of October had around 3,200 kilograms (7,000 pounds) of uranium enriched to 3.5 percent level, and nearly 40 kg of the material refined to 20 percent level, according to the IAEA.

Salehi’s remarks were seen as reaction to comments by US Secretary of State Hillary Clinton in Abu Dhabi on Monday when she asserted Iran’s nuclear programme has been hit by sanctions.

*”They have made it much more difficult for Iran to pursue its nuclear ambitions,”* she said. *”Iran has technological problems that have made it slow down its timetable.”*

Salehi also dismissed reports that the nuclear programme was hit by the Stuxnet computer virus, which the New York Times said on Saturday was tested by Israel and US on Tehran’s nuclear installations.

*”The Stuxnet issue goes back a year and a half. When they initiated this, they thought we were sleeping… If this was effective, the IAEA, which regularly inspects (the sites) would have reported the slowdown of our activities,”* he said.

In its online edition, the Times quoted intelligence and military experts as saying Israel has tested the effectiveness of the Stuxnet computer worm, which apparently shut down a fifth of Iran’s nuclear centrifuges in November and helped delay its ability to make its first nuclear weapons.

The testing took place at the heavily guarded Dimona complex in Israel’s Negev desert housing the Middle East’s sole, albeit undeclared nuclear weapons programme.

*”To check out the worm, you have to know the machines,”* a US expert told the newspaper. *”The reason the worm has been effective is that the Israelis tried it out.”*

There has been widespread speculation that Israel was behind the Stuxnet worm that attacked computers in Iran.

Those participating in the tour of Iranian atomic sites are representatives of the Non-Aligned Movement troika, the Group of 77, the Arab League, Syria, Venezuela and Oman, according to the Iranian envoy to the IAEA, Ali Asghar Soltanieh.

The tour has been snubbed by the European Union, and by Iran’s key allies Russia and China. Iran did not invite the United States, Britain, France and Germany.

Such visits to Iran’s atomic sites are infrequent. The last trip that Tehran arranged for members of the IAEA was in February 2007.