Iran faces a possible fourth round of U.N. Security Council sanctions due to its uranium enrichment work which Western nations believe is designed to develop a nuclear bomb.
Tehran denies the charge and says its atomic program is only for civilian purposes.
"We confirmed that if we do not see a constructive answer from Iran, we will have to discuss this in the U.N. Security Council," Russian Foreign Minister Sergei Lavrov told reporters at a news conference with his German counterpart in Berlin.
He added that he still hoped to find a diplomatic solution.
Earlier, German Foreign Minister Guido Westerwelle said Iran had used delaying tactics instead of taking action.
"For the past two years Iran has repeatedly bluffed and played tricks," Westerwelle told Deutschlandfunk radio. "It has played for time and of course we in the international community cannot accept a nuclear-armed Iran."
Iranian President Mahmoud Ahmadinejad said on Tuesday his country was ready to send low-enriched uranium (LEU) abroad to be converted into fuel for a Tehran nuclear medicine reactor to show its nuclear aims were purely peaceful.
Beijing said on Thursday this signaled a shift in Iran's position which meant it was worth continuing negotiations rather than discussing broader sanctions against Tehran. But diplomats said Iran had not conveyed any change in its stance to the IAEA.
China and Russia have tended to be more reluctant than other U.N. Security Council permanent members to further penalize Iran. But recent comments, including Lavrov's latest, indicate Moscow may be increasingly ready to agree to sanctions.
In Washington, U.S. Secretary of State Hillary Clinton said pressure from the five permanent U.N. Security Council members and Germany, the "P5+1," had helped move negotiations forward.
"They've helped to enable the negotiations to go forward by joining with very strong language about what was expected from Iran," she said, referring to the group made up of the United States, Britain, France, China, Russia and Germany.
"The fact is we haven't really seen much in the way of response. Sometimes we see response from a part of the government that is then retracted from another part of the government."
MUNICH MEETING
Lavrov said he planned to meet Iranian Foreign Minister Manouchehr Mottaki on the sidelines of the Munich Security Conference, which starts later on Friday, and that he saw a chance to narrow differences with Iran in talks.
"I will try to convey the position of the (six world powers) about the need for Iran to answer the International Atomic Energy Agency's (IAEA) questions and take certain steps that would assure us of the exclusively peaceful nature of Iran's nuclear program," said Lavrov.
"The questions the IAEA has placed before Iran are not complicated."
An agreement on practical issues, such as the question of uranium supplies for Iran's nuclear research reactor, would change the atmosphere and create conditions for renewing negotiations between the six world powers and Iran, said Lavrov.
The United States, Britain, France, Germany, China and Russia have long sought to agree how best to persuade Iran to cooperate on its nuclear program.
"I hope … a concrete, constructive reaction will follow," said Lavrov, due to address the Munich conference on Saturday.
(Additional reporting by Brian Rohan and Steve Gutterman in Moscow; Writing by Madeline Chambers; Editing by Jon Boyle)
