BEIJING — Kai Li, an American businessman born in China, had stepped off a plane in Shanghai, preparing to visit his mother’s grave. Instead, Chinese state security officers grabbed him and accused him of spying, and a court later sentenced him to 10 years in prison after a short, secretive trial.

Now, two and a half years after Mr. Li was detained, his family in New York has broken its silence, saying that the espionage conviction against Mr. Li, an exporter of aircraft parts, was groundless and driven by political motives.

In recent years, relations between the United States and China have been tested by trade and technology disputes. The United States has accused China of hacking companies and inducing or bribing scientists to hand over commercial secrets. China has also stepped up warnings against foreign spies and publicized convictions of foreigners on espionage charges.

Harrison Li, Mr. Li’s son, said the Chinese authorities had charged his father with providing state secrets to the F.B.I. He says he is sure that his father was not a spy, and that his conviction showed the risks that American visitors to China face as tensions with the United States have festered.