"Grave concern" by US over Iran's nuclear defiance

WASHINGTON (AFP) - The United States expressed "grave concern" Tuesday over Iran's defiance in ramping up its nuclear capability amid new estimates by the UN atomic agency that the Islamic republic could have 8,000 centrifuges enriching uranium by December.

The significant rise in Iran's nuclear capability is likely to fuel fears that Tehran seeks nuclear weapons, diplomats close to the International Atomic Energy Agency (IAEA) said in Vienna Tuesday.

IAEA chief Mohamed ElBaradei has been telling political leaders in private conversations that Iran shows no sign of slowing down in its uranium enrichment, a process that can be used to make nuclear fuel but also atomic weapons, one diplomat said.

"It's a source of grave concern to the international system that they persist in this behavior in defiance of the will of the international community, the Security Council, the IAEA Board of Governors," State Department spokesman Sean McCormack told reporters.

He said the international community had to make it "clear to Iran that it can't persist in this behavior, that they have to change course, and that failure to change course is only going to result in greater isolation" and more punitive sanctions.

ElBaradei's estimate of Iran obtaining 8,000 centrifuges was based on "the technical assessment of his inspectors" and so was sound, another diplomat close to the IAEA said.

The United States is stepping up moves with its allies for a third set of UN Security Council sanctions against Iran, which again failed to obey a Security Council deadline to suspend uranium enrichment.

The sanctions over the past half year target Iran's ballistics and nuclear industries.

The United States accuses Iran of seeking nuclear weapons, but Iran insists its nuclear drive is entirely peaceful and it just wants to generate energy for a growing population.

Washington says it wants a diplomatic solution to the nuclear question but has not ruled out a military intervention and has placed sizeable naval forces in the Gulf.