President Barack Obama vowed yesterday the United States will ratchet up pressure on Iran in a unified global stand, as Tehran said it had persuaded Beijing sanctions were no longer necessary.

Only hours after urging Chinese President Hu Jintao to join forces to ensure Iran reins in its suspect nuclear programme, Mr Obama put the Islamic regime on notice that a drive for fresh UN sanctions was gathering pace.

"I have said before that we don't take any options off the table, and we're going to continue to ratchet up the pressure and examine how they respond," he told CBS television.

"But we're going to do so with a unified international community - that puts us in a much stronger position."

The US President warned of "huge destabilising effects in the region" if Iran acquires the capacity to make nuclear weapons, just hours after he talked to Hu in a rare call from Air Force One and "underscored the importance of working together."

"All the evidence indicates that the Iranians are trying to develop the capacity to develop nuclear weapons," Mr Obama told CBS.

Iran has fiercely denied allegations that it is seeking to develop an atomic bomb, saying its contested nuclear enrichment programme is purely for peaceful purposes.

Chief Iranian nuclear negotiator Saeed Jalili yesterday warned the West to stop "threatening" Tehran after talks in China - one of the six world powers leading negotiations with Iran.

And he suggested that Beijing was heeding Tehran's calls for help.

"We jointly emphasised during our talks that these sanctions tools have lost their effectiveness," Mr Jalili said after meeting Chinese officials including Foreign Minister Yang Jiechi and State Councillor Dai Bingguo.

Although he said reporters "must ask China their position," he added that "China accepted Iran's position."

The Chinese foreign ministry did not immediately respond to an AFP request for comment.

But Yang said China "urges relevant parties to step up diplomatic efforts, and show flexibility, to create the conditions to resolve the Iranian nuclear issue through dialogue and negotiation," the foreign ministry said yesterday.

Mr Jalili also warned the West to back off, predicting that otherwise the talks would collapse.

"If they continue with simultaneous talks and pressure, these negotiations cannot succeed," Mr Jalili said. "China as a large country can play an important role in changing these wrong methods."

Beijing so far has been the most hesitant member of the P5+1 group - Britain, China, France, Russia, the US and Germany - over calls to impose a fourth set of UN sanctions on Iran.

But Mr Jalili's claims that he had won China's backing ran counter to a growing quiet confidence among US officials that Beijing was gradually being swayed over to its side.

The US ambassador to the United Nations, Susan Rice, and US Secretary of State Hillary Clinton, have both said this week that Beijing was ready to join in the Security Council talks.

And on Thursday the Obama administration said it was pleased China had agreed to sit down at the United Nations and discuss toughening the sanctions on the Islamic republic.

Spokesman Bill Burton said the move proved that despite lingering "disagreements we can work together on issues like nuclear proliferation."