For years, U.S. officials have accused China of stealing American technology to design and build fighter planes. But while China learned how to build advanced fighters, its pilots could not fly them so well.

That may be starting to change, according to American officials.

U.S. and allied intelligence officials warned on Wednesday that Beijing was intensifying a campaign to entice former fighter pilots from Western nations to train Chinese pilots.

The United States, Britain, Canada, Australia and New Zealand — an intelligence-sharing partnership known as the Five Eyes — said in a bulletin that China’s People’s Liberation Army was trying to tap the “skills and expertise of these individuals” to improve its own air operations.

“To overcome their shortcomings, China’s People’s Liberation Army has been aggressively recruiting Western military talent to train their aviators, using private firms around the globe that conceal their P.L.A. ties and offer recruits exorbitant salaries,” said Michael C. Casey, the director of the U.S. National Counterintelligence and Security Center.

China has been building up its air and naval forces, and leaders in Beijing have warned that they could eventually be open to using force to unite their country with Taiwan. American officials, speaking on the condition of anonymity to discuss the findings, say there is little doubt that Chinese fighter pilots appear to be getting better.

But officials debate how much of the improvement can be attributed to training by foreign pilots versus an increase in hours that Chinese pilots are logging in homegrown training programs.