"Our first conditions are the freezing, suspension of uranium enrichment. The approach of the six (powers) is that Iran should suspend enrichment only for the period in which talks continue," Lavrov told Interfax and ITAR-TASS news agencies.
Lavrov, speaking after talks in London among the five permanent members of the United Nations Security Council plus Germany, said there had been no discussion of imposing new sanctions on Iran.
"There wasn’t anything about new sanctions although our American colleagues take the view that pressure on Iran must be maintained.
"Its necessary to explain to Iran the advantages it would receive from agreeing to start talks, on the basis of one condition -- the freezing of uranium enrichment," Lavrov said.
He added that the parties meeting in London had discussed earlier proposals put forward by Iran encompassing nuclear energy, trade and investment and regional security issues.
Western powers fear Tehran wants to use its nuclear programme to make atomic weapons but the Islamic republic insists the drive is peaceful and solely aimed at providing energy for a growing population.
The six have been seeking to persuade Iran to rein in its nuclear work using a mix of incentives and sanctions.