Military action against Iran would be a "very serious mistake fraught with unpredictable consequences", Russia's foreign minister has warned.
Sergei Lavrov said diplomacy, not missile strikes, was the only way to solve the Iranian nuclear problem.
His comments come after Israeli President Shimon Peres said an attack on Iran was becoming more likely.
The UN's atomic watchdog is expected to say this week that Iran is secretly developing a nuclear arms capability.
Diplomats say the International Atomic Energy Agency (IAEA) report, due for release on Tuesday or Wednesday, will produce compelling evidence that Iran will find hard to dispute.
Iran has always insisted that its nuclear programme is exclusively to generate power for civilian purposes.
Iranian Foreign Minister Ali Akbar Salehi has said the alleged evidence is a fabrication and part of a multi-pronged US smear campaign against his country.
