The United States said a deal signed on Monday between Switzerland and Iran's state gas firm sends "precisely the wrong message" amid the continued crisis over Tehran's nuclear programme.

"We have conveyed to the Swiss that major new oil and gas deals with Iran send precisely the wrong message at a time when Iran continues to defy UN Security Council resolutions," the US embassy in Bern said in a statement.

Swiss Foreign Minister Micheline Calmy-Rey signed the agreement with her Iranian counterpart Manouchehr Mottaki in Tehran on Monday.

Financial details were not disclosed but the contract between Iran's state gas firm and Switzerland's Elektrizitaets-Gesellschaft (EGL) Laufenburg reportedly envisages Iran supplying 5.5 billion cubic metres (194 trillion cubic feet) of gas annually from 2011.

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The US embassy said it believes the deal "violates the spirit of the sanctions" imposed on Iran by the UN Security Council in a bid to try to force Iran to give up its programme of uranium enrichment and cooperate further with the International Atomic Energy Agency (IAEA).

"We are disappointed, and will continue our discussions with the Swiss regarding the need to maintain pressure on Iran to meet its international obligations," the US statement said.