An influential Iranian cleric praised recent nuclear talks between Iran and world powers on Friday, the latest in a series of positive statements from senior figures that analysts said could signal Tehran is softening its stance.

Ayatollah Ahmad Jannati, secretary of the powerful Guardian Council, said the talks showed 'success and progress' but added Tehran would break off the negotiations if Western countries carried on imposing sanctions while negotiating.

World powers held talks with Tehran in Istanbul last week over their concerns about its nuclear programme, which the US and its allies say is a cover for developing an atomic weapons capability.

Iran has refused to stop enriching uranium, despite pressure from Western sanctions, and says its nuclear work is for purely peaceful purposes.

Western diplomats reacted to the meeting with cautious optimism but said there was a long way to go before any deal could be done. The two sides agreed to meet again in Baghdad on May 23.

Addressing Friday prayers, Jannati said the talks showed 'success and progress', adding: 'They (western countries) are ready to accept that enrichment is Iran's right,' state media reported.

He added Iranians needed assurances from the West that it would no longer be their enemy.

'The West should lift sanctions against Iran but if they continue to insist on sanctions and then say they are negotiating with Iran, it is clear that this talks will be halted,' he warned.

Although his comments took a typically anti-Western tone, analysts say they were a further sign of a changing attitude within the Iranian leadership.

Earlier this week Foreign Minister Ali Akbar Salehi said Iran was 'ready to resolve all issues very quickly and simply'. His words were echoed by parliamentary speaker Ali Larijani and senior MP Alaeddin Boroujerdi.

'Iran will bargain inch by inch in Baghdad but there is a genuine desire to reach an agreement,' said Sadeq Zibakalam, a professor of political science at Tehran University, who was optimistic that a deal could be reached eventually.

'They are paving the way and preparing the public for a deal with the West. But the language is about trying to maintain that it is not a submission and that they haven't given in.'

While other analysts were less sanguine about prospects of a deal, they agreed Tehran had altered its strategy.

'It seems to be that they are trying to shape the talks through public diplomacy. I think they are certainly looking for a deal but I am not sure they are going to get it,' said Professor Ali Ansari of Scotland's St Andrews University.

'They are definitely trying to change the narrative.'

Sounding a more sceptical note, one western diplomat earlier this week told Reuters the change of tone was welcome but said Iran might just be trying to buy more time.

Analysts and some diplomats have told Reuters in recent weeks both sides must compromise for any chance of a long-term settlement, suggesting Iran could be allowed to continue limited low-level enrichment if it accepts more intrusive U.N. nuclear inspections.

They added Iran might be prepared to consider an updated proposal of a 2009 fuel swap deal that collapsed when the two sides failed to agree on the details of implementation.

In a change from past failed negotiations, Iran has also hinted progress could be made if the sanctions imposed by the United States and the European Union were reviewed.

The U.S. Congress has recently debated a further round of sanctions against Iran's energy, shipping, and mining sectors but President Obama has not yet commented on them.-Reuters