WASHINGTON, March 26: The United States on Monday criticised Iran's partial suspension of cooperation with the UN nuclear watchdog agency, calling it a “step in the wrong direction” while reports in the international media said that any military strike on Iranian nuclear installations will have to be carried out before the end of the year.

US State Department deputy spokesman Tom Casey told reporters in Washington that despite the UN-sponsored sanctions announced on Saturday, the so-called five plus one group is still willing to engage Iran if it shows flexibility on the uranium enrichment issue.

The group includes five permanent members of the Security Council and Germany who are willing “to engage in negotiations with the Iranians should they choose to go in that direction,” Mr Casey said.

“Unfortunately,” he added, “President (Mahmoud) Ahmadinejad seems intent on taking Iran down the wrong path.”

Iran announced on Sunday that it would partially suspend co-operation with the UN's International Atomic Energy Agency in response to the Security Council vote.

Iranian President Mahmoud Ahmadinejad said the latest sanctions would not halt the country's uranium enrichment “even for a second”. As they “stem from the hostility by some powers against Iran”.

“It is not a new issue for the Iranian nation. Enemies of the Iranian nation have made a mistake this time, too,” he said.

Meanwhile, reports in the international media that by the end of this year, Iran would be able to enrich uranium to level that it would no longer be possible to attack its nuclear sites.

Any strike on a site with enriched uranium will have serious radiation fallout, said that report, adding that any attack on Iranians may have to be carried out before the end of the year.

The reports said that while Iran is still several years away from making nuclear weapons, by the end of the year Iran would have enriched weapons-grade material in sufficient amounts to trigger a nuclear catastrophe if hit.

The reports suggested that Iran is attempting to produce a critical mass of enriched uranium before the end of the year. Any attack after that would risk triggering fallout that could kill civilians over large distances and make parts of Iran uninhabitable.

The same consideration figured in the timing of Israel's attack on Iraq's nuclear reactor in 1981.