U.S. Republican presidential nominee Sen. John McCain (R-AZ) greets supporters during a rally in Toledo, Ohio October 19, 2008. REUTERS/Carlos Barria

UNITED NATIONS (Reuters) - John McCain’s U.S. presidential election campaign has solicited a financial contribution from an unlikely source -- Russia’s U.N. envoy -- but a McCain spokesman said on Monday it was a mistake.

In the letter, McCain urged Russia’s U.N. Ambassador, Vitaly Churkin, to contribute anywhere from $35 to $5,000 to help ensure McCain’s victory over Democratic rival Sen. Barack Obama, currently ahead in voter preference polls.

“If I have the honor of continuing to serve you, I make you this promise: We will always put America -- her strength, her ideals, her future -- before every other consideration,” McCain assured Churkin.

Moscow’s mission to the United Nations issued a terse statement on the Republican presidential candidate’s letter, saying that the Russian government and its officials “do not finance political activity in foreign countries.”

A spokesman for McCain, a long-time critic of Russia, had a simple explanation for the fundraising letter’s arrival at the Russian mission in New York: “It was an error in the mailing list.”

The letter was addressed to Churkin and sported a McCain signature near the bottom.

Earlier this month, both McCain and Obama harshly criticized Russia for invading Georgia two months ago, but neither was willing to say yes when asked if Russia under Prime Minister Vladimir Putin was the “evil empire”.

It is illegal for U.S. presidential candidates to accept funds from foreign sources. The McCain campaign accused Obama earlier this month of not doing enough to screen for illegal contributors and asked U.S. election officials to investigate.

McCain has agreed to public financing for his campaign and therefore cannot accept funds from private donors.