The Russian foreign minister has warned that a Western military strike against Iran would be "a catastrophe".
Sergei Lavrov said an attack would lead to "large flows" of refugees from Iran and would "fan the flames" of sectarian tension in the Middle East.
Israeli Defence Minister Ehud Barak earlier said any decision on an Israeli attack on Iran was "very far off".
Meanwhile, Iran's foreign minister said talks on its nuclear programme would "most probably" take place in Istanbul.
Ali Akbar Salehi told reporters during a visit to Turkey that negotiations were going on about venue and date, and the timings would be settled soon.
But the UK Foreign Office said that there were "no dates or concrete plans" for talks, as Tehran had yet to respond to a letter from EU foreign policy chief Baroness Ashton and demonstrate that it would negotiate without preconditions, according to the Reuters news agency.
Talks between Iran and six world powers - the US, UK, China, France, Russia and Germany - were last held in Istanbul a year ago but no progress was made.
Tensions with Iran have risen in recent weeks after the UN's nuclear monitors confirmed Tehran was producing 20% enriched uranium at its Fordo plant near Qom.
The US and its allies suspect the Islamic Republic of secretly trying to develop a nuclear weapons capacity but Iran insists its programme is peaceful.
The US has recently imposed sanctions on Iran's central bank and against three oil companies which trade with the country. The European Union has said it will place an embargo on Iran's oil exports.
For its part, Iran has threatened to block the transport of oil through the Strait of Hormuz, a key shipping route.
Israel - thought to be the only nuclear power in the region - has said it could launch a military strike against Iran to prevent it developing nuclear weapons.
Last week, Iran blamed Israel and the US for the death of Mostafa Ahmadi-Roshan, an Iranian nuclear scientist apparently killed by a bomb targeting his car in Tehran.
BBC diplomatic correspondent Jonathan Marcus says Mr Barak's comments can be seen as an attempt to placate the Americans, who are growing concerned that Israel may take military action against Iran without alerting Washington in advance.
The comments from Russia's foreign minister included criticism of the Western moves to strengthen sanctions on the Islamic Republic, which he said were aimed at "stifling" Iran's economy.
Mr Lavrov told journalists in Moscow that they would have to ask those who he said were "talking constantly" about a military attack to find out if it would occur. He said such an attack would start off a "chain reaction" and he did not know how that would end.
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