Pakistan has begun moving its nuclear weapons in low-security vans on congested roads to hide them from US spy agencies, making the weapons more vulnerable to theft by Islamist militants, two US magazines reported Friday.

The Atlantic and the National Journal, in a joint report citing unnamed sources, wrote that the US raid that killed Al-Qaeda chief Osama bin Laden in May at his Pakistani compound reinforced Islamabad's longstanding fears that Washington could try to dismantle the country's nuclear arsenal.

As a result, the head of the Strategic Plans Divisions (SPD), which is charged with safeguarding Pakistan's atomic weapons, was ordered to take action to keep the location of nuclear weapons and components hidden from the United States, the report said.

Khalid Kidwai, the retired general who leads the SPD, expanded his agency's efforts to disperse components and sensitive materials to different facilities, it said.

But instead of transporting the nuclear parts in armored, well-defended convoys, the atomic bombs "capable of destroying entire cities are transported in delivery vans on congested and dangerous roads," according to the report.

The pace of the dispersal movements has increased, raising concerns at the Pentagon, it said.

Pakistan has long insisted its nuclear arsenal is safe and the article quotes an unnamed official from the powerful Inter-Services Intelligence agency saying: "Of all things in the world to worry about, the issue you should worry about the least is the safety of our nuclear program."

The Pentagon declined to comment on the article but a senior US military official told reporters in Washington Friday that the United States remains confident Pakistan's nuclear weapons are secure.

"I believe the Pakistan military arsenal is safe at this time, well guarded, well defended," said the military official, who spoke on condition of anonymity.

The article, based on dozens of interviews, said the US military has long had a contingency plan in place to disable Pakistan's nuclear weapons in the event of a coup or other worst-case scenario.

The Joint Special Operations Command (JSOC) has for years trained for a potential "disablement campaign" that its forces would lead and that would require entering more than a dozen nuclear sites and seizing or defusing atomic weapons, it said.

The operation would use sensitive radiological detection devices that can pick up trace amounts of atomic material and JSOC has even built mock Pashtun villages with hidden mock nuclear-storage depots at a site on the East Coast to train elite Navy SEAL and Delta Force commandos, the report said.

Although Pakistan has suggested it might shift towards China and forsake its ties to Washington, Chinese officials have reached an understanding in secret talks with US representatives that Beijing would raise no objections if the United States opted to secure Pakistan's nuclear weapons, said the report, citing unnamed US sources.