By Barbara Plett,
BBC News, Islamabad
Pakistan has raised the state of alert around its nuclear facilities amid concerns they could be targeted by Islamist militants.
Pakistan insists its nuclear armoury will not be compromised
But a senior Pakistan military official said there had been no specific threat to the sites, and insisted that safeguards in place were fool proof.
The official was speaking in a rare press briefing on the issue.
It followed Western media reports warning that Pakistan's nuclear weapons could fall into the wrong hands.
The Pakistani authorities have been angered by Western media reports speculating that the country's nuclear arsenal could fall into the hands of al-Qaeda militants.
The senior military official briefing foreign journalists said that the weapons were protected by an elaborate command and control system, and multiple levels of security.
He acknowledged that Islamic militants had begun to attack army personnel in recent months, and that nuclear sites may also become a target.
He said the state of alert around nuclear facilities had increased, but there had been no specific threats against them.
The official said there was no way the Taleban or al-Qaeda could take over Pakistan's estimated 50 nuclear warheads.
And he dismissed the possibility of collusion from within the system, saying all personnel dealing with sensitive material had been carefully monitored.
Despite fears raised by US media and politicians, the official said the US administration had not shown any recent concern about the safety of Pakistan's nuclear weapons.
He also said any foreign intervention over the issue would be disastrous for the intruder.