LONDON - Between ten and 20 countries will likely soon develop the capacity to build nuclear weapons unless major powers take steps to disarm, the head of the UN's nuclear watchdog said in an interview.

In an interview with the Guardian newspaper, IAEA chief Mohamed ElBaradei predicted a surge in the number of "virtual nuclear weapons states" who can produce plutonium or highly enriched uranium and know how to make warheads.

While they would likely stop short of assembling a weapon, thus remaining technically compliant with the nuclear non-proliferation treaty (NPT), they could be within a couple of months of deploying and using a nuclear bomb.

"This is the phenomenon we see now and what people worry about in Iran. And this phenomenon goes much beyond Iran," said ElBaradei, director general of the International Atomic Energy (IAEA).

"Pretty soon... you will have nine weapons states and probably another 10 or 20 virtual weapons states."

Western powers fear Iran is secretly trying to build nuclear weapons, a charge denied by Tehran, which says its nuclear programme is for civilian use.

ElBaradei, who is due to leave his job in November, said the regime built around the 1970 NPT to stop the spread of nuclear weapons risked collapse.

"Any regime ... has to have a sense of fairness and equity and it is not there," he told the Guardian.

He added: "We still live in a world where if you have nuclear weapons, you are buying power, you are buying insurance against attack. That is not lost on those who do not have nuclear weapons, particularly in [conflict] regions."

ElBaradei expressed most concern about the spread of nuclear technology in the Middle East, which he said was a "ticking bomb".

The only solution was for established nuclear powers to disarm as rapidly as possible and pass internationally agreed bans on nuclear tests and on the production of weapons-grade fissile material, he said.

"If some of this concrete action is taken before the NPT [conference next April], you would have a completely different environment " he said.

"All these so-called virtual weapons states, or virtual wannabe weapons states, will think twice ... because then the major powers will have the moral authority to go after them and say: 'We are doing our part of the bargain. Now it is up to you."