Even after a string of UN sanctions, the assassination of its scientists and a computer bug attacking its systems, Iran is still defiantly pressing ahead with its nuclear programme.

So a number of think-tanks are coming out and urging the West to seize on new signals from Tehran, repeated last week, that it might be prepared to halt the most sensitive area of its activities.

This is the enrichment of uranium to 20-percent purity, something Iran began doing last year, taking it closer to the 90-percent level that could potentially be used in a nuclear weapon, experts say.

Iran plans to triple output and is moving its production to a difficult-to-bomb mountain bunker, and although analysts differ on how close Iran is to actually having The Bomb, most agree on the direction.

The most alarmist prediction is from Greg Jones of the US-based Nonproliferation Policy Education Center, who thinks Iran could make enough fissile material within eight weeks of deciding to do so. By the end of 2012, it could take just four weeks.

Olli Heinonen, IAEA inspections head until 2010 and now at the Belfer Center for Science and International Affairs at Harvard Kennedy School, thinks it won't have enough material before 2013 -- although it could do sooner if Iran starts using "better machines."

This date though "is only for the fissile material. You have to distinguish between the weapon itself, the design, and we don't know where they are... and an entirely different ballpark is the delivery. As I understand it the missile programme is lagging behind," he told AFP.

The International Atomic Energy Agency (IAEA) said in September it was "increasingly concerned" about a possible military dimension, about which it "continues to receive new information."

Next month, the nuclear watchdog might flesh out these claims in a new report, and the agency's board could decide -- although this is seen by analysts as uncertain -- to report Tehran again to the UN Security Council.

Almost three years since then-new US President Barack Obama offered an "extended hand" to Iran, tensions rose further this week as Washington accused Tehran of being behind an alleged plot to kill the Saudi ambassador.

Iranian President Mahmoud Ahmadinejad's declarations last month on the sidelines of a UN General Assembly, repeated last week, that Tehran was ready "immediately" to stop enriching to 20 percent therefore caught some attention.

In return, Ahmadinejad says he wants fuel assemblies imported for use in the Tehran Research Reactor, which produces medical isotopes for cancer patients.

Ali Vaez and Charles D. Ferguson, both from the Federation of American Scientists (FAS), urged the West to accept and provide fuel to Tehran -- and without conditions.

The proposal, they wrote in the New York Times, was a "rare chance to move forward" and to cut the "Gordian knot that has stalled the West's negotiations with Iran."

The Washington-based Institute for Science and International Security (ISIS), too, said it would be "wise" to pursue the offer, proposing that a "modest" deal be struck over two years.

Mark Fitzpatrick at the London-based International Institute for Strategic Studies (IISS) meanwhile told AFP that the chances of success for such a deal are "rather low, but the West should listen and pursue a discussion with Iran over it."

Details are lacking. It is unclear, for example, if Iran has in mind sending its stockpiles of enriched uranium abroad, as proposed in a similar 2009 deal that fell victim, analysts believe, to power battles in Tehran.

For now, the West remains unimpressed.

After Ahmadinejad's UN appearance, US State Department spokeswoman Victoria Nuland said the offer "looks like a diversion from the real issues," and added the Iranian president "makes a lot of empty promises."

Fellow Security Council permanent member France, whose President Nicolas Sarkozy warned Tehran on August 31 of the risk of a "preventive strike", said last Wednesday that it wanted "actions", not words from Iran.