Iran and world powers on Tuesday dug in for a second day of attritional talks in Moscow aimed at breaking an increasingly risky deadlock in the decade-long crisis over the Iranian nuclear programme.

With the United States and Israel refusing to rule out military action and Tehran facing severe economic sanctions, the price of failure in the Russian capital could be high but there was no sign of progress on the first day.

Negotiators from the six world powers asked Iran to scale back its enrichment of uranium, a process which can be used to make nuclear fuel but also the explosive core of a nuclear bomb.

But Iran's chief nuclear negotiator Saeed Jalili responded with a five-point powerpoint presentation listing Iran's own demands, an EU official said, apparently leaving both sides talking at cross purposes.

"The main stumbling block is the fact the positions of the sides are rather complicated and hard to reconcile," the Interfax news agency quoted Deputy Foreign Minister Sergei Ryabkov as saying after Monday's first round.

EU delegation spokesman Michael Mann indicated all had not been harmonious: "We had an intense and tough exchange of views," he said.

The two sides opened the second day of plenary talks at 0800 GMT after the Iranian side had bilateral discussions in the morning with the Russian delegation and the world powers held their own internal meeting to coordinate strategy, delegates said.

The Iranians are expecting their counterparts to come up with answers to the points that had been laid out the day earlier while the world powers want to see some sign of flexibility from Iran.

"The P5+1 group will today announce its position on Iran's proposals, and specifically about the issue of Iran's enrichment right," Jalili's deputy Ali Bagheri told the Mehr news agency.

The world powers are the so-called "P5+1" -- permanent UN Security Council members Britain, China, France, Russia and the United States, plus Germany -- with their negotiating team led by EU foreign policy chief Catherine Ashton.

Mann said that world powers had repeated the demand at the last session of talks in Baghdad last month that Iran stops enriching uranium to 20 percent, a degree approaching the level required in nuclear weapons.

The Islamic Republic however "brought up lots of questions and well-known positions, including past grievances," he added.

Iran has repeatedly over the last years insisted it has every right to enrich uranium but it remains to be seen if it could accept a compromise solution and enrich uranium to a lesser degree of around five percent.

The talks mark a rare show of unity between the West and Russia. After their meeting in Mexico Monday, US President Barack Obama and Russian President Vladimir Putin jointly warned Iran it must comply with its nuclear obligations.

Iran must "undertake serious efforts aimed at restoring international confidence in the exclusively peaceful nature of its nuclear programme," they said.

The Iranian negotiators late Monday held an evening meeting with Russia's National Security Council chief Nikolai Patrushev, a close Putin ally.

The West has long accused Iran of seeking an atomic bomb under the guise of a civilian nuclear energy programme, a charge vehemently denied by Tehran. Host Russia has long taken a more cautious line, saying Iran must restore confidence but not explicitly accusing it of military intentions.

If Iran accepted the demands of world powers to scale down enrichment, it would in return receive some forms of peaceful nuclear energy cooperation from the West and much needed spare-parts for its embargo-hit aviation sector.