Washington accused Pakistan's largest nuclear facility of sharing technological know-how to make weapons of mass destruction or missiles capable of delivering them, a U.S. Embassy spokeswoman said Monday.

Linda Cheatham said another country was involved and refused to say which. But a North Korean firm, Changg Wang Sinyong Corp., was also slapped with sanctions, apparently for its alleged role in missile transfers with Pakistan.

On Tuesday, Pakistan denied the allegations and demanded Washington provide proof.

"This is absolutely baseless. We ask America to come up with whatever evidence they have to prove what they are saying," Information Minister Sheikh Rashid Ahmed told The Associated Press Tuesday by telephone.

"We have neither imported and/or exported nuclear technology to anyone," Ahmed said.

The Bush administration imposed two-year sanctions on Khan Research Laboratories, or KRL, Cheatham said. The sanctions took effect Monday and ban all U.S. sales and contracts with the laboratory.

In recent months Pakistan has fended off renewed charges that it sold its nuclear technology to North Korea in exchange for the Nodong missile.

Pakistan's Ghauri missile series -- tested last October and capable of carrying a nuclear payload deep into India -- is a copy of North Korea's Nodong missile, the Federation of American Scientists has said.

Cheatham said the lab allegedly made "material contributions" to another country's efforts to "use, acquire, design, develop and/or secure weapons of mass destruction, and/or missiles capable of delivering weapons."

The Federation of American Scientists describes the KRL as Pakistan's main nuclear weapons laboratory where uranium is enriched.

Earlier this year, Secretary of State Colin Powell sought assurances from Pakistan's President Pervez Musharraf that the there was no help between Pakistan and North Korea.