– North Korean scientists have learned to produce crucial components of gas centrifuges inside their isolated country, undermining years of export controls and sanctions intended to stop the country's enrichment of uranium for nuclear weapons, according to an analysis by two U.S. arms control experts made available Monday.

The analysis comes as experts have reported other signs that North Korea is activating or expanding its nuclear production facilities. Taken together, they suggest a new effort by the North to master all the facets of the nuclear production cycle — or perhaps to give the impression of nuclear progress that would drive new offers of talks or economic aid, in the view of some analysts.

The new study focuses on production of advanced centrifuges, a technically difficult feat that the United States and others have tried to make more difficult for the North with a network of sanctions and bans on the export of sophisticated parts and metals.

If the North Koreans are making their own parts, they would essentially invalidate much of the international strategy to force them to denuclearize and make it more difficult to monitor their production progress.

"That means, unfortunately, that we won't be in a good position to spot them expanding the program through foreign shopping expeditions, and that policies based on export ­controls, sanctions and interdiction won't get much traction, either," said Joshua Pollack, one of the experts presenting the findings this week. "The deeper implication, if they are able to expand the program unchecked, is that we'll never be too confident that we know where all the centrifuges are. And that in turn could put a verifiable denuclearization deal out of reach."

Pollack's findings in collaboration with Scott Kemp, an expert on centrifuge technology at MIT, will be presented Wednesday during a conference organized by the Asan Institute for Policy Studies in Seoul.

Pollack said he and Kemp had analyzed such open-source data as scientific journals, news reports and propaganda from North Korea. They found evidence that the country is learning — or has already learned — how to make such crucial centrifuge components and related technologies and materials as uranium hexafluoride, vacuum pumps, frequency inverters, magnetic top bearings and maraging steel. He said that domestic production appeared to have begun no later than 2009.

North Korea shocked the United States in 2010 when its officials escorted U.S. nuclear expert Siegfried S. Hecker of Stanford University to their main nuclear complex in Yongbyon, north of Pyongyang. There, they showed him a modern plant that they said housed 2,000 gas centrifuges, a technology that North Korea said it would use to enrich uranium for reactors but that U.S. officials feared was a cover for making highly enriched uranium for atomic bomb fuel.

Then, this April, at the height of tensions incited by the North's nuclear test in February, the country declared that it would "adjust and alter the use of the existing nuclear facilities" for "bolstering up the nuclear armed force both in quality and quantity." It said that included immediately restarting the Yongbyon facilities.

The Institute for Science and International Security in Washington cited satellite images last month to report that North Korea appears to have doubled the size of the building that housed the uranium enrichment plant in Yongbyon in recent months, and raising concerns that its enrichment capability would grow along with it.