Top Pentagon officials have said that the security of Pakistan's nuclear weapons are not under threat despite the current political crisis, but have maintained that the United States will have to be very careful about it.

"I know there has been a lot of discussion about the security of the nuclear weapons. I had like to be very clear. I do not see any indication right now that security of those weapons is in jeopardy, but clearly we are very watchful, as we should be," the chairman of the Joint Chiefs of Staff Mike Mullen said in a press conference.

"As far as operations are concerned, our military-to-military contacts and dialogue between leaders continue, and I have seen no disruption of that as a result of the emergency measures in place. I have also not seen and do not anticipate any interruption of the logistics through Pakistan at this point," he said.

"No major changes to our military relationship with Pakistan. We had certainly like to see the emergency measures end as soon as possible. But I believe militarily the situation is stable," Admiral Mullen said.

Meanwhile, Defence Secretary Robert Gates said: "I am not aware that we have either asked or received from the Pakistanis any reassurances. I have the sense people are comfortable."

"I am not going to make a call. I would say, though, that his ability to lead, to continue to be a partner in the war on terror very much depends on how developments unfold over the next few weeks in Pakistan. He needs to move beyond the emergency measures as quickly as possible," Gates said, adding, "I think our view is he needs to step out of army chief of staff role and become a civilian."