SEOUL, South Korea — 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 American arms control experts made available on 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 harder for the North with a network of sanctions and bans on the export of sophisticated parts and metals. If the North Koreans are successfully 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.