"I am as comfortable as I can be that they have taken significant steps, including steps in recent years to improve the security with respect to their nuclear weapons," Admiral Mike Mullen, Chairman of the US Joint Chiefs of Staff told reporters during a luncheon with Pentagon Press Association.
At the same time he conceded that there are limits to what he know and to what anybody outside Pakistan knows.
"But I know that they have invested a great deal, improved their procedures and they take it very seriously," he said.
The US Government, he noted, has made investment in the safety and security of these nuclear weapons.
"There have been investments made by our governments in improving security, not through the Department of Defense, but through the Department of Energy to improve security through the last several years. We have seen it physically, be more secure," Mullen said.
"We have seen the training improve, if you will. They have introduced in recent years, I am not sure what they would call, it would be equivalent to what we call personnel reliability programme, which is a very difficult screening process which we go through and in our own nuclear weapons program and routinely update and have to have compliance with," he said.