MOSCOW — Russia disclosed on Wednesday that Russian and Chinese envoys had pressed Iran’s government to accept a United Nations plan on uranium enrichment during meetings in Tehran early this month but that Iran had refused, leaving “less and less room for diplomatic maneuvering.”

“The clouds are piling up,” said a top Russian Foreign Ministry official, briefing reporters on condition of anonymity, following diplomatic protocol. He said Russia would consider supporting sanctions tailored to prevent the spread of nuclear weapons, though it “is certainly against any paralyzing sanctions that are aimed not at nonproliferation but at punishing Iran or, God forbid, regime change.”

At the United Nations, Mark Lyall Grant, the British ambassador, confirmed that political directors from the six countries that could approve sanctions against Tehran had consulted by telephone on Wednesday and that China had finally “agreed to engage substantively on the issue.”

Li Baodong, the new Chinese ambassador, emphasized that China is committed to the Nuclear Nonproliferation Treaty. “We think it’s very important to maintain stability and peace in the Middle East,” he told reporters, but he left ambiguous exactly what China is committing to.