Russian Foreign Minister Sergei Lavrov made it clear Thursday that Moscow wouldn't back any new rounds of tough sanctions against Iran in the United Nations Security Council, and he dismissed a U.S. timetable for securing progress from Iran on ending its nuclear-fuel program.

Lavrov's comments in Moscow cast doubt over the ability of the U.S. to succeed in an effort to secure international backing for new sanctions. They also appeared to end any hopes that the Obama administration's "reset" of troubled relations with Russia would lead to Moscow's support for one of the top U.S. foreign policy priorities.

Just a day after U.S. officials warned that Iran may already have enough enriched uranium to make a bomb if processed further, Lavrov said negotiations should begin without any imposed timetable. He also said that even if Iran tried to make weapons-grade fuel it would be detected and there would be time to respond.

"I do not think those sanctions will be approved by the United Nations Security Council," Lavrov said.

President Barack Obama has set a deadline of September for progress on talks with Iran, and the U.S. and its allies have planned to work on an international consensus by the end of the month when the United Nations General Assembly meets in New York, with Obama playing host. But Russia wields a veto on the 15-member council.

"We're pretty disappointed with the Russian position so far," a senior U.S. official said of Lavrov's comments. Officials said any new U.N. sanctions against Iran were now unlikely in the near term, and said their best hope would be to coordinate new financial penalties with the members of the European Union instead.

Click here to read more on this story from the Wall Street Journal.