TEHRAN (Reuters) - Russia urged Iran on Tuesday to comply with demands by the United Nations Security Council to curb its nuclear program, but Tehran was defiant.

The Russian comments underlined Moscow’s commitment to tackle Tehran after the Security Council passed a resolution on Monday imposing a third round of sanctions on Iran for its refusal to suspend sensitive nuclear activities.

Russia and China have been lukewarm about taking tough action on Iran compared with the European Union and with the United States, which fears it is seeking a nuclear bomb.

“This resolution is a serious political signal to Tehran about the need to cooperate with the U.N. Security Council,” Russia’s Foreign Ministry said in a statement.

The resolution imposed more travel and financial curbs on Iranian individuals and companies, expanded a ban on trade in items with both civilian and military uses, and called for increased vigilance over Iranian financial institutions.

Tehran, which has ignored all Council demands to freeze its uranium enrichment program, rejected the new resolution.

“This resolution ... has been issued based on political motives and hostile orientations and lacks value, is unacceptable and condemned,” Foreign Ministry spokesman Mohammad Ali Hosseini was quoted by IRNA news agency as saying.

President Mahmoud Ahmadinejad said that “the Iranian nation’s fearlessness and resistance is viewed favorably in all countries of the world.”

Iran says its work on uranium enrichment -- which can produce fuel for nuclear power plants or atomic weapons -- is part of a program meant purely to generate electricity.

It has previously dismissed the impact of sanctions, saying it has a cushion of crude revenues thanks to windfall earnings as the world’s fourth largest oil producer.

But business executives say the measures are making foreigners increasingly wary of investing in Iran, slowing down major oil and other projects, and pushing up trading costs as more foreign banks avoid dealings with the Islamic Republic.

TRADE WITH CHINA

Diplomats said the new sanctions were a moderate tightening and the most Washington could get after a U.S. intelligence report said Iran had scrapped an atom bomb program in 2003.

“We were pleased yesterday to see that the U.N. Security Council went forward with a third round of sanctions,” White House spokeswoman Dana Perino said. “A lot of people thought that wasn’t going to be possible after our National Intelligence Estimate came out in December ...”

Efforts to curb Tehran’s nuclear program have been driven by permanent Security Council members the United States, Britain and France, working along with Germany.

Permanent members Russia and China have resisted strong sanctions, which they say would make Iran unwilling to cooperate on international safeguards meant to stop nuclear proliferation.

China, an increasingly important commercial partner as Western businesses scale back dealings with Tehran, said the new sanctions would not affect its trade with Iran.

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Chinese Foreign Ministry Spokesman Qin Ganghe told a news conference his country’s trade ties with Iran “have no correlation with Iran’s nuclear plans and also do not go against the U.N. Security Council’s resolutions”.

Russia’s Foreign Ministry said the U.N. resolution was “an uneasy compromise” from which all the “excessive political and economic demands by hardliners” had been dropped.

It urged permanent Council members, plus Germany, to “demonstrate their readiness for serious cooperation with Iran.”

But it also said: “We expect Iran’s leadership to analyze thoroughly the declaration by the six foreign ministers as well as the contents of the adopted resolution, and opt in favor of meeting demands by the International Atomic Energy Agency (IAEA) and Security Council.”

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WORRIES OVER WEAPONISATION

In Geneva, Iranian Foreign Minister Manouchehr Mottaki reiterated an Iranian assertion that a February 22 report by the IAEA had cleared up questions about its nuclear program, and said there was no justification for the sanctions.

IAEA Director Mohamed ElBaradei denied this on Monday. He said improved Iranian transparency had settled some questions, but intelligence suggesting Tehran was trying to “weaponise” nuclear materials remained a pressing issue.

Weaponisation usually refers to the process of making nuclear warheads for delivery on missiles. Iran said the intelligence was fabricated by the United States.

While Iran and the IAEA disputed the details, ordinary people in Tehran said they were the ones who were suffering from rising prices that they blamed on the sanctions.

White House spokeswoman Perino said: “It’s unfortunate for the Iranian people that their regime continues to isolate them in this way, but that’s the choice that their regime has made.”

Asked whether Washington would push for a fourth round of sanctions, she said: “We just finished the third round, so I think let’s see. I think the most important next step is that countries implement the sanctions and make sure that they follow through on that obligation.”

(Additional reporting by Dmitry Solovyov in Moscow, Ben Blanchard in Beijing, Hossein Jaseb in Tehran and Stephanie Nebehay in Geneva)