Fears over bin Laden 'dirty bomb'

American intelligence chiefs fear terror mastermind Osama bin Laden was far closer to a crude atomic bomb than they had believed, it emerged today.

US spies have found evidence bin Laden and his al-Qaida network had made strides towards producing a device known as a dirty bomb.

The bomb does not use a nuclear explosion but conventional means to spread large doses of radiation over a wide area.

The disclosure in today’s Washington Post newspaper comes after the interrogation of captured al-Qaida operatives and evidence gathered in Afghanistan by CIA agents and American special forces troops.

And recent American intelligence reports have described a meeting where one of bin Laden’s associates showed the terror chief a canister allegedly containing radioactive material.

The American government has now asked some of its allied governments to check if the associate, who has a common name, could have entered their countries with the material.

And some countries have taken the report so seriously they are stepping up the use of devices that measure radioactivity at their border, the newspaper reported.

Bin Laden has made clear in the past he believes it his ‘‘sacred duty’’ to obtain nuclear, chemical and biological weapons to further the ‘‘jihad’’ or ‘‘holy war’’ he has unilaterally launched against America and its allies.

Last month he told a Pakistani newspaper he had nuclear weapons, a claim which American officials doubt.

‘‘I wish to declare that if America used chemical or nuclear weapons against us, then we may retort with chemical and nuclear weapons,’’ bin Laden was quoted as saying.

‘‘We have the weapons as a deterrent.’’

But Abdul Salam Zaeef, former Taliban ambassador to Pakistan, said: ‘‘We do not even have modern weaponry, not to mention weapons of mass destruction.’’

The new evidence has prompted American security officials to be so concerned about the threat that they told visiting foreign officials they could not meet Vice-President Dick Cheney face-to-face because of the possibility al Qaida could have a ‘‘dirty bomb’’.

And worry that the terror network could have obtained the bomb were part of the reason that the FBI issued a security alert to all 18,000 American police forces on Monday night, a source told the newspaper.

The weapon, also known as a radiological bomb, can be made by wrapping readily-available conventional explosives around highly-radioactive material, such as spent fuel rods from nuclear reactors.

If detonated it would create a zone of intense radiation that could extend up to a mile around the blast site, leading to radiation sickness and cancer in people caught in it.

No evidence has been found of any country exploding such a bomb and there has been no firm proof al-Qaida has produced it, but a diagram of such a device was found in a Taliban or al-Qaida facility in Afghanistan in recent weeks.

Russia and Pakistan are considered the two most likely sources of radioactive material for bin Laden.

Russian officials have reported dozens of attempts to steal enriched uranium or plutonium since 1990, while there have been claims its scientists have sold expertise and equipment to rogue states including Iraq and North Korea.