The US has warned Iran that it will not escape being referred to the UN Security Council if it proceeds with its plan to conduct sensitive nuclear work.
The administration of US President George W. Bush said on Tuesday it was "in close contact" with its partners, including Britain, Germany and France, discussing a response to Iran's removal of UN seals from equipment that is being used to enrich uranium.
"If the regime in Iran continues on the current course ... there is no other choice but to refer the matter to the Security Council," White House spokesman Scott McClellan told reporters.
At present, he added, the US is "in close contact with the Europeans and others about how to move forward" at the International Atomic Energy Agency (IAEA).
McClellan said Bush for now has no intention of launching an attack against Iran to prevent it from acquiring nuclear weapons, adding that, however, the military option remained on the table.
McClellan also reminded reporters of numerous statements issued on the subject by Bush.
For the time being, the spokesman pointed out, the Bush administration is working with the international community to resolve the issue by peaceful and diplomatic means and intends to continue doing so.
The US administration did not say if the talks focused on convening an emergency meeting of the IAEA, the UN nuclear watchdog group.
Nor did it say whether the US will throw all its weight behind attempts to persuade the UN Security Council to take up the measure after two fruitless years of European-led negotiations to persuade Iran to abandon uranium enrichment.
"I think we are entering a period of intense diplomatic activity on this question," said a senior State Department official who spoke on condition of anonymity.
"There are intense discussions at the political director level, and I will expect we will see more and more discussions at the minister level," the official said.
By removing seals on equipment inside the Natanz nuclear plant located in central Iran, Tehran showed its determination to at least partly resume its uranium enrichment activities.
However, the West may now believe Iran has crossed the line.
That is how Westerners who for months have been pressing Iran to end its enrichment activities were interpreting the decision to remove the seals.
Gregory Schulte, the US' ambassador to the IAEA, said earlier that Iran was "taking another deliberate step toward uranium enrichment, the process for creating nuclear bomb material."
"By cutting the seals, the Iranian leadership shows its disdain for international concern and its rejection of international diplomacy," Schulte said in a statement.
Both White House and State Department spokesmen mentioned "a serious escalation" on the part of Iran regarding the nuclear issue.
The US, which has repeatedly made clear it has no doubt Iran wants to acquire nuclear weapons, has been a long and active advocate of referring the matter to the UN Security Council.
Since 2003, Washington has reluctantly allowed the EU's attempt to persuade Iran to provide guarantees that its nuclear program is of a purely civilian nature.
The question now is whether Washington has really concluded that Tehran has gone too far and whether it will be able to convince Moscow and Beijing to support it in the Security Council.