The UN atomic agency's second visit to Iran in a month next week could be Tehran's "last chance" to show goodwill on its nuclear programme and avoid sanctions, but analysts and diplomats are less than hopeful.

After a first visit on January 29-31 produced few results, the International Atomic Energy Agency (IAEA) announced it would return to Tehran on February 20-21.

"I'm not optimistic that Iran will provide much more information because I think any honest answers to the IAEA's questions would confirm that Iran had been involved in weapons-related development work and Iran wouldn't want to admit that for fear of being penalised," Mark Fitzpatrick of the London-based International Institute for Strategic Studies told AFP.

The West has long contended that Iran is seeking the atomic bomb and insists it comply with UN Security Council resolutions to halt enriching uranium, but Tehran says its nuclear programme is merely for civilian purposes.

Failure to make at least some concessions next week could bring about new pressure on Iran, which has already been targeted by four sets of UN sanctions and a series of unilateral US and EU measures.

"The second meeting will be a last chance for Iran to make a significant gesture," said Mark Hibbs, of the Carnegie Endowment for International Peace.

If IAEA chief Yukiya Amano writes in his report to the agency's board of governors in March that Tehran did not cooperate, "that could trigger additional pressure from the Western group in the board on a resolution that would again raise the temperature, call for more sanctions."

"The IAEA report will be more condemnatory if Iran does not demonstrate some flexibility by answering some questions and it knows that, it will try to give the IAEA some basis for pulling its punches," Fitzpatrick added.

Two of the main points of contention after the first visit were Iran's refusal to allow the IAEA access to certain nuclear sites and scientists, as it had requested.

"At this point we expect it (the second visit) will be more of the same," a Western diplomat in Vienna told AFP.

"Absent any real cooperation, answering the questions and allowing the access, the meetings are just meetings, it's just talk... We don't have very high expectations at this point."

British Foreign Secretary William Hague warned on Friday that Iran's nuclear ambitions could trigger "a new Cold War" more perilous than that between the West and the Soviet Union,

"If (the Iranians) obtain nuclear weapons capability, then I think other nations across the Middle East will want to develop nuclear weapons," he told Britain's Daily Telegraph newspaper.

Ahead of the IAEA visit, Tehran went into a flurry of activity this week, announcing advances in its nuclear work -- including the addition of 3,000 more centrifuges to its uranium enrichment effort and the introduction of new generation centrifuges that would speed up enrichment -- and making a long-awaited overture to Western powers to resume stalled talks.

The United States dismissed the technical breaks as "hyped" and a show of bravado.

"Iran is clearly feeling the pressure of its international and diplomatic isolation," said State Department spokeswoman Victoria Nuland.

But for some, this could also be a bargaining chip as Iran prepares to return to the negotiating table.

"This announcement establishes facts on the ground in advance of any negotiation that Iran may have with the P5+1 (the five permanent members of the UN Security Council and Germany)," and could be rolled back as concessions if needed, said Hibbs.

France, the US and the European Union cautiously welcomed a February 14 letter by Iran saying it was ready to resume P5+1 nuclear talks -- which broke down a year ago -- at the "earliest" opportunity.

And analysts predicted this could happen very quickly.

Nevertheless, the catalogue of grievances against Iran is long.

In a November report, the UN watchdog said it had information that "indicates that Iran has carried out activities relevant to the development of a nuclear device."

Iran also started enriching uranium to 20-percent purity in January, taking it significantly closer to the 90-percent mark needed for a nuclear bomb.

Meanwhile, Israel, the sole -- albeit undeclared -- nuclear power in the region, has accused Tehran of masterminding a series of bomb attacks on its diplomats in Georgia, Thailand and India this week.

The IAEA team, led by chief inspector Herman Nackaerts, will leave Vienna for Tehran late Sunday for its two-day visit.