Talks between world powers and Iran to defuse the Iranian nuclear crisis face a tough future after the sides failed to edge any closer to a breakthrough at a crunch meeting in Moscow, analysts said.

Negotiators from the six world powers and their Iranian counterparts managed at the talks on Monday and Tuesday to prevent the diplomatic process from complete collapse by agreeing a new expert-level meeting in Istanbul on July 3.

But with Iran defying Western demands to scale down its sensitive uranium enrichment activities and the West showing no sign of lifting sanctions, it is unclear how much room for manoeuvre is left for the new talks.

The Moscow round came at a critical moment in the decade-long nuclear crisis, with Tehran about to face potentially crippling EU and US sanctions against its oil sector and the option of military action still on the table.

"Some narrowing may have occurred, but going forward talks will take place against the background of a new round of escalation and counter escalation," said Trita Parsi, president of the National Iranian American Council.

"That will further render an agreement difficult," said Parsi, author of the book "A Single Roll of the Dice" on American diplomacy with Iran.

The world powers known as "P5+1" -- permanent UN Security Council members Britain, China, France, Russia and the United States, plus Germany -- failed to win any concession from Iran that would give the talks a new impulse.

The West suspects Iran of seeking to make nuclear weapons under the guise of an energy programme and wants it to stop enriching uranium to 20 percent purity -- a level close to that needed to make the core of a nuclear bomb.

But Western powers have also refused to concede to Iranian demands to scrap US and EU sanctions targeting its oil export sector that are due to come into force on June 28 and July 1 respectively.

French Foreign Minister Laurent Fabius said hours after the talks ended that sanctions against Tehran should "continue to be tightened as long as Iran refuses to negotiate seriously."

"The crucial sanctions-lifting bit is missing and some Western states won't agree to do that unless Iran moves first," commented Mark Hibbs of the Carnegie Endowment for International Peace.

"But Iran isn't willing to do that, so there is no movement."

Further complicating the picture is that within the P5+1 Russia and China are firmly opposed to the unilateral US and EU sanctions. "All six are not on the same page on this issue," Hibbs said.

Previous rounds in Istanbul and Baghdad also resulted in no progress. The latest talks -- led by chief Iranian negotiator Saeed Jalili and EU foreign policy chief Catherine Ashton -- were a struggle, Western officials said.

"We went round and round for quite a while," said a senior US administration official, speaking on condition of anonymity.

The only firm outcome of the talks was the agreement for the lower-level meeting in Istanbul. This would be followed by a meeting between Ashton and Jalili's deputies and then the top envoys themselves. But no dates were set.

"Continuing the talks on the experts level will not solve the issue," said Mohammad Saleh Sedghian of the Tehran-based Arabic Centre for Iranian Studies.

"If the talks continue at the current level or lower, as was decided, we should be looking at a marathon of talks with no end."

But it also appears the Iran's foes are already using other methods, away from negotiation. Iran was recently hit by a massive cyberattack by a malware known as Flame able to steal documents, according to industry experts.

The Washington Post reported Tuesday that the United States and Israel collaborated on creating the virus to spy on Iran's computer networks and send back intelligence used for an ongoing cyberwarfare campaign.

Sedghian the West was for the moment happy to pressure Iran with the sanctions and cyberwarfare since it is "much cheaper than the military option which will burden the US, Israel and the Western allies".