Pakistan opposes a nuclear and conventional weapons arms race in South Asia, a Foreign Ministry spokeswoman said on Monday.
But Tasnim Aslam also declined to reject a report saying the country was expanding its atomic arms capabilities.
Monday's Washington Post cited independent analysts as saying Pakistan had started work on a new reactor at its Khushab atomic site.
The move, the paper said, could signal a major expansion of the country's nuclear weapons capabilities.
"This ought to be no revelation to anyone because Pakistan is a nuclear weapon state." Aslam said. "(But) I have no specific comments on Pakistan's facilities."
Aslam defended Pakistan, saying it was not the first country to introduce nuclear weapons into South Asia.
The comment apparently referred to archrival India, with whom this Muslim nation has fought three wars with since 1947.
"We were not the first to test nuclear weapons in this region and that remains our position," Aslam said during a press conference. "We do not want an arms race in this region."