The State Department has denounced a Chinese court’s sentencing of a prominent journalist, Dong Yuyu, to seven years in prison and said it stood with his family in calling for his “immediate and unconditional release.”

A court in Beijing announced the sentence on Friday for his conviction on charges of espionage. Mr. Dong, 62, a former Harvard Nieman fellow, has been held since February 2022, when officers from the Ministry of State Security, China’s main intelligence agency, detained him and a Japanese diplomat while they ate lunch in a restaurant.

The officers released the diplomat after an interrogation, but prosecutors put Mr. Dong on trial behind closed doors in July 2023. He is the most prominent journalist imprisoned in mainland China.

Matthew Miller, the State Department spokesman, said in a statement on Friday that Mr. Dong’s “arrest and today’s sentencing highlight the P.R.C.’s failure to live up to its commitments under international law and its own constitutional guarantees to all its citizens.” He used the initials of the formal name of the country, the People’s Republic of China.

“We celebrate Dong’s work as a veteran journalist and editor, as well as his contributions to U.S.-P.R.C. people-to-people ties, including as a Harvard University Nieman fellow,” Mr. Miller added. “We stand by Dong and his family and call for his immediate and unconditional release.”

R. Nicholas Burns, the U.S. ambassador to China and a former Harvard professor, also issued a statement of condemnation, calling the sentencing “unjust.”