The United States believes that Pakistan's nuclear weapons are in safe hands, a State Department spokesman said Wednesday, rebutting a report that Islamabad's atomic arsenal was vulnerable to theft.

Two US publications, The Atlantic and the National Journal, citing unnamed sources, last week said Pakistan had transported nuclear weapons in low-security vans on congested roads to hide them from US spy agencies.

State Department spokesman Mark Toner told reporters in Washington that the United States was not persuaded that safety had been compromised.

"We have confidence that the government of Pakistan is well aware of the range of potential threats to its nuclear arsenal and is accordingly giving very high priority to securing its nuclear weapons and materials effectively," Toner told reporters.

"We continue to have confidence... that they're taking appropriate steps," he said.

Pakistan at the weekend rejected as "pure fiction" the report's assertion that transporting the weapons in such a manner had made them more susceptible to theft by Islamist militants.