The foreign ministry summoned the new Swiss ambassador, Walter Haffner, on the same day he presented his credentials, to express the Jewish state's "regret" over the deal, it said in a statement.

"Switzerland and the international community are aware of the danger from Iran. Israel expects Switzerland to adhere to the international efforts on this issue," the ministry said.

"While the international community works to make Iran abandon its nuclear programme, Israel believes this is not the right moment for economic deals with Iran."

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 Laufenburg reportedly envisages Iran supplying 5.5 billion cubic metres (194 trillion cubic feet) of gas annually from 2011.

Israel considers Iran its top enemy following repeated calls by President Mahmoud Ahmadinejad for the Jewish state to be wiped off the map.

Israel, widely considered to be the Middle East's sole if undeclared nuclear power, and its main US ally suspect Tehran of trying to develop atomic arms under the guise of its nuclear programme, a charge Iran denies.

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