WASHINGTON — 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, according to a draft report by a former top U.N. arms inspector that suggests the plans could have been shared secretly with any number of countries or rogue groups.

The drawings, discovered in 2006 on computers owned by Swiss businessmen, 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 report states.

The computer contents — among more than 1,000 gigabytes of data seized — were recently destroyed by Swiss authorities under the supervision of the U.N. nuclear watchdog agency, which is investigating the now-defunct smuggling ring previously led by a Pakistani scientist, Abdul Qadeer Khan.

But U.N. 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 who spent four years researching the smuggling network, said.

“These advanced nuclear weapons designs may have long ago been sold off to some of the most treacherous regimes in the world,” Mr. Albright writes in a draft report about the blueprint’s discovery. A copy of the report, expected to be published later this week, was provided to the Washington 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, Mr. Albright said in his report. While Libya was given plans for an older and relatively unsophisticated weapon that was bulky and difficult to deliver, the newly discovered blueprints offered instructions for building a compact device, the report said. The lethality of such a bomb would be little enhanced, but its smaller size might allow for delivery by ballistic missile.