JERUSALEM, March 19 (Reuters) - Israel lodged a complaint with Switzerland on Wednesday over a Swiss-Iranian natural gas purchase, calling the deal inconsistent with U.S.-led efforts to curb Tehran's nuclear programme through economic isolation.

Swiss Foreign Minister Micheline Calmy-Rey announced the sale during a visit to Tehran on Monday and said her country was ready "to contribute to solutions" to the stand-off over Iranian uranium enrichment and other sensitive nuclear projects.

Israel's Foreign Ministry said in a statement that it summoned Swiss Ambassador Walter Haffner to deplore Calmy-Rey's trip to Iran, calling it "an act that is unfriendly to Israel".

Given recent U.N. Security Council sanctions against Iran, "now is not the proper time to pursue economic deals" with the government of President Mahmoud Ahmadinejad, the statement said.

Ahmadinejad has questioned the Holocaust and called for the Jewish state to be "wiped of the map", stirring war fears. Iran says its nuclear programme is for energy, not military, ends.

The Swiss energy group that signed the 25-year purchase said it could be worth between 10 billion euros ($13.32 billion) and 22 billion euros, depending on factors such as the price of oil.

Calmy-Rey said the contract was "important in a long-term perspective" for both sides and added it did not violate U.N. sanctions resolutions.

"Switzerland and the entire international community are aware of the danger posed by Iran. Israel expects Switzerland to join the international effort in this matter," the Israeli Foreign Ministry statement said.

Israel is assumed to have the region's only atomic arsenal.

Last year, diplomats said Switzerland had proposed a staged plan leading to a simultaneous suspension of Iran's uranium enrichment work and of U.N. sanctions, which would enable talks between Iran and six world powers to begin. (Writing by Dan Williams; Editing by Matthew Jones)

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