Nicholas Burns, Under Secretary of State for Political Affairs, underlined that Iran was responsible for breaching an accord struck with the EU in Paris last November, under which it pledged to freeze the sensitive atomic action.

"I think the ball's in Iran's court more than it is in the EU's court," said Burns, whose government suspects Tehran of trying to develop atomic weapons under the guise of its civilian nuclear program.

"Here is a country that unilaterally ruptured the Paris agreement ... that has resumed conversion in Isfahan ... a country that seems to be embarked in a very radical course," he added.

Talks with the so-called EU-3 -- Britain, France and Germany -- broke down in August, when Iran slammed the door on an offer of incentives in exchange for a cessation of fuel work.

Iran also ended a freeze on fuel cycle work by resuming uranium conversion -- a precursor to potentially dual-use enrichment work.

In September, the 35-nation board of the International Atomic Energy Agency (IAEA) passed a resolution finding Iran to be in non-compliance with the Nuclear Non-Proliferation Treaty (NPT) -- paving the way for the matter to be referred to the UN Security Council.

Under the NPT, to which Iran is a signatory, non-nuclear-weapon states undertake not to acquire or produce nuclear weapons or nuclear explosive devices.

They are required also to accept safeguards to detect diversions of nuclear materials from peaceful activities, such as power generation, to the production of nuclear weapons or other nuclear explosive devices.

Burns stressed the importance of the IAEA resolution. "Our view is that the pressure is really on the Iranian government to respond to this very strong vote," he said.

"The Iranians are in a weakened position diplomatically and it is up to the Iranians to come back to these negotiations with the EU-3 and to resume them."

He reiterated Washington's support for the EU's diplomatic efforts. "Our instinct is to let the EU-3 be in the lead and to support the EU-3 and try to resume negotiations," he said.

But he warned: "If the Iranians cannot do that they will face increased diplomatic pressure and further isolation."

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.