China's refusal to sign on to new sanctions against Iran risks prompting a backlash affecting its increasingly complex interests abroad, experts say.

Recent remarks by President Barack Obama citing China's opposition, and unusually tough talk from Russia _ long a sanctions skeptic _ has spotlighted Beijing's refusal to back such steps as a way of pressuring Iran over its nuclear program.

Nikolai Patrushev, the chief of Russia's Security Council, said Tuesday that Iran's recent actions "have raised doubts among other nations, and these doubts are quite well-founded." His comments appeared to indicate that Russia is increasingly warming up to the U.S. sanctions push.

The U.S. and France said Iran's announcement that it would enrich uranium to 20 percent left no choice but to push harder for a fourth set of U.N. Security Council sanctions to punish Iran's nuclear defiance. Iran said Tuesday it had started enrichment under U.N. supervision.

However, China _ which relies on Iran for energy supplies _ maintains that now isn't the right time to discuss such measures and that the door to negotiations with Tehran remains open. As a permanent member of the Security Council, along with the U.S., Russia, Britain and France, China is in a position to veto any new measures.

The opposition is part of an increasingly assertive _ even aggressive _ Chinese diplomacy that is drawing growing concern from Washington and in Europe.

Among steps taken, Beijing this month threatened to withhold cooperation on international issues of concern to the U.S. in retaliation over Washington's approval of a $6.4 billion arms sale to Taiwan, the self-governing island that China considers a part of its territory.

Western analysts warn, however, that such a stance risks denting China's international reputation, damaging relations with the European Union, and triggering muscular reprisals from Washington, for whom the Middle East is a foreign policy linchpin.

Among possible responses, Washington could decide to sell Taiwan even more weaponry, such as fighter aircraft that the island has requested, wrote Ralph Ralph Cossa, president of the Pacific Forum CSIS think tank, in a a recent foreign policy brief

Meanwhile, Washington could dial back its willingness to ensure Chinese interests in Iraqi oil contracts and Afghan copper mining if Beijing is seen as obstructing U.S. efforts on the crucial Middle Eastern diplomatic landscape, said Georgia Tech expert John Garver.

"How can Beijing expect the U.S. to respect China's interests, when Beijing violates U.S. vital interests?" Garver said.

World powers fear the Iranian nuclear program might be a cover for building atomic weapons. Iran says the program is peaceful and aims to generate power for its growing population.

Conflict over Iran would almost certainly send world oil prices soaring, inflicting pain on China's economy at a time when the government is spending hundreds of billions of dollars to stimulate growth. If the U.S. and others were to deploy sanctions on their own, Chinese companies that deal with Iran could find themselves barred from business in other nations.

China depends on oil- and gas-rich Iran for 11 percent of its energy needs and last year became Tehran's biggest trading partner, according to Iranian figures. Trade volume reached at least $36.5 billion, the Iran-China Chamber of Commerce reported, with Iran mainly importing consumer goods and machinery from China and exporting oil, gas, and petrochemicals.

Chinese companies also have major investments in Iranian energy extraction and the construction of roads, bridges and power plants.

Beijing's main concern over sanctions is that they will go too far, ultimately harming those economic ties, said Yin Gang, an expert on Iran at the Chinese Academy of Social Sciences.

"China has economic and trade relations with Iran, so it's natural that China would not want to see regional security and its own national interests affected due to excessive sanctions," Yin said.

In addition, Beijing believes past measures to punish Iran have been largely ineffective, said retired diplomat Hua Liming.

"China and the international community have all seen that the sanctions have not changed Iran's decision to carry on the nuclear program," Hua said.

"On the contrary, sanctions will take the already complex and tense situation in the Middle East to a more dangerous stage, which is something China does not wish to see," he said.