"We know how to defend our nuclear assets," Foreign Office spokesman Mohammad Sadiq was quoted as saying by the state-run APP news agency.

He was reacting to a report in British newspaper The Herald, which quoted military sources as saying that a US Special Forces squad and volunteer scientists from the Nuclear Emergency Search Team had orders to take control of Pakistan's estimated 60 nuclear warheads dispersed around six to 10 high-security military bases to prevent them falling into the hands of ‘Islamic extremists’.

The report also said some of the US forces were already in neighbouring Afghanistan to ‘seize or disable’ Pakistan's nuclear weapons in the event of the collapse of the administration following the killing of Bhutto.

Sadiq rejected the report as ‘baseless and ridiculous’, saying Pakistan has an effective command and control system.

"People circulating such sinister stories are aiming at further upsetting the people of Pakistan, who are still in a state of shock after the assassination of former Prime Minister Benazir Bhutto in a dastardly attack on December 27."

A US Embassy official, requesting not to be named, too said, "any such action would be contrary to our long standing military and diplomatic cooperation with Pakistan".