Iran today said it would resume the manufacture of nuclear fuel and warned of greater instability in the Middle East if the UN Security Council (UNSC) imposes sanctions.
US officials said yesterday they still want to bring Iran before the UNSC, but have not yet been assured of EU backing.
Washington argues that Tehran is making fuel for atomic warheads. Iran insists it intends to use enriched uranium only in power stations. The EU currently favours negotiating with the Iranians over international concerns that a weapons programme is in development.
"If the Americans succeed in referring Iran's case to the Security Council, Iran will immediately suspend all its voluntary confidence-building measures," Iran's chief nuclear negotiator Hassan Rohani said.
Iran agreed last year to suspend making nuclear fuel for a few months while it held talks with Britain, France and Germany. The EU states are encouraging Iran to drop its fuel programme in return for economic incentives.
"Parliamentarians may even come up with a harder decision," Mr Rohani added, in reference to the rump of Iranian parliamentarians who want the Islamic state to withdraw from the international nuclear Non-Proliferation Treaty (NPT).
In the shorter term they have threatened that Iran will not ratify the Additional Protocol to the NPT, which permits snap UN inspections of nuclear sites.
"The security and stability of the region would become a problem," said Mr Rohani, a mid-ranking cleric who is secretary-general of Iran's Supreme National Security Council.
"This would be a particular problem for the United States because it has a lot of troops and equipment in region and is in fact our imposed neighbour."
Iran often complains that it feels besieged by the United States, which has troops in Iraq and Afghanistan and has conducted military exercises in the Caspian Sea. But Mr Rohani still held out hope that talks with Europeans could pay dividends, saying Iran had given the Europeans "an objective guarantee" that it was not seeking to manufacture nuclear warheads.
He said any European position asking for an end to the enrichment uranium to make nuclear fuel was unacceptable. Iran-EU talks continue in Geneva next week.