Russia will try to shield its ally Iran from the looming threat of military strikes while seeking an elusive commitment on its nuclear programme when it hosts showdown talks on the crisis next week.

A skilled balancing act would put a rare feather in Moscow's diplomatic cap and support its arguments in an increasingly confrontational standoff with the West over Iran's strife-torn partner Syria.

But failure may only further erode Russia's slipping Middle East standing while creating even more uncertainties about how to address building concerns about the military aspects of Iran's purportedly peaceful nuclear drive.

The stakes could thus hardly be higher when two days of talks between Iran and the five permanent UN Security Council members plus Germany begin Monday under the watchful eye of President Vladimir Putin -- a strongman who expects results.

"The Iranians are coming under a lot of pressure from Russia not to screw this up on their watch," said one Western official familiar with the situation.

"Russia's position will get firmer if Iran refuses to negotiate," added Andrei Baklitsky of the PIR Centre for non-proliferation studies.

"That would be a diplomatic slap in Russia's face."

The urgency for Iran is being compounded by the July 1 deadline the European Union has slapped on a full oil embargo and the June 28 rollout of tough US sanctions against a host of world countries that buy Iranian oil.

Yet divisions within Iran itself and a bruising second round of talks in Baghdad last month leave some observers thinking that Moscow will need to work a minor miracle to keep the talks alive.

The sceptics particularly cite this month's failed meeting with the IAEA nuclear watchdog and the difficulty US President Barack Obama will have in making any concessions with elections approaching in November.

"Of course there is a certain time limit," said a senior European diplomat.

"If there is a collective assessment that it is not going anywhere, we will have to say no to talks for talks' sake."

Russia's Kommersant daily said the threat of the process falling apart forced Foreign Minister Sergei Lavrov to decide last weekend to pay a flash visit to Tehran on Wednesday for a meeting with chief negotiator Saeed Jalili.

Iran followed that announcement by quickly saying it was now willing to discuss the same package proposal it had found unacceptable in Baghdad.

The deal would see the Islamic Republic stop enriching uranium to 20 percent -- seen as being just steps away from weapons-grade -- and ship out its existing stock while also shuttering its forbidden Fordo bunker.

The tough terms would not lead to the quick lifting of sanctions but instead see the West extend some forms of peaceful nuclear energy cooperation and provide assistance for Iran's battered aircraft industry.

Europe would also help Iran export oil to key client Asia by easing an EU tanker insurance ban.

The plan is in line with the "step by step" approach promoted by Moscow and underscores the periodic suspicions that have clouded relations since the 1829 murder by a Tehran mob of the tsar's ambassador to the Persian Empire.

Putin pointedly stressed during the brief public portion of his meeting with Iranian President Mahmoud Ahmadinejad in Beijing last week that "we are very strong supporters of the non-proliferation of nuclear weapons."

Russia has seemingly tried to play down expectation by noting last weekend that "we obviously understand that the sides will not be able to agree on all issues in Moscow.

"But we proceed on the assumption that the negotiating process must by all means continue after the Moscow round," the Russian foreign ministry said.

Analysts said the question of whether this happens depends mostly on the extent to which Iran feels it can still count on Russia once the full range of oil sanctions sets in.

"I generally avoid using the expression 'last chance' meeting, but the Moscow one may be turning into a showdown given the July 1 sanctions deadline," said Bruno Tertrais of the Paris-based Foundation for Strategic Research.