A report compiled by a former UN arms inspector warns that an international smuggling ring that sold bomb-related parts to Libya, Iran and North Korea also managed to acquire blueprints for an advanced nuclear weapon, The Washington Post reported Sunday.

The newspaper said a copy of the draft it had obtained suggests the plans could have been shared secretly with a number of countries or rogue groups.

The study focuses on drawings discovered in 2006 on computers owned by Swiss businessmen, according to the paper.

They included essential details for building a compact nuclear device that could be fitted on a type of ballistic missile used by Iran and more than a dozen developing countries, The Post said.

The computer contents -- among more than 1,000 gigabytes of data seized -- were recently destroyed by Swiss authorities under the supervision of the International Atomic Energy Agency, which is investigating the now-defunct smuggling ring previously led by Pakistani scientist Abdul Qadeer Khan.

But UN officials cannot rule out the possibility that the blueprints were shared with others before their discovery, the report's author, David Albright, a prominent nuclear weapons expert, told The Post.

"These advanced nuclear weapons designs may have long ago been sold off to some of the most treacherous regimes in the world," the paper quotes Albright as saying in his report.

A copy of the report, expected to be published later this week, was provided to The Post.

The A.Q. Khan smuggling ring was previously known to have provided Libya with design information for a nuclear bomb.

But the blueprints found in 2006 are far more troubling, Albright said, because they offered instructions for building a compact device.

The lethality of such a bomb would not be significantly enhanced, but its smaller size might allow for delivery by ballistic missile, the paper said.