BEIJING (Kyodo) -- A former senior editor at a major Chinese newspaper affiliated with the ruling Communist Party pleaded not guilty Monday to leaking information to Japanese diplomats in an appeal trial after receiving a seven-year jail term for espionage, sources familiar with the matter said.

Dong Yuyu, a former deputy head of the Guangming Daily editorial department, submitted to the first hearing of the appeal trial at a Beijing court a letter from Japanese Ambassador to China Kenji Kanasugi. In the letter, Kanasugi denied Japanese diplomats were spies, thereby supporting Dong's plea of innocence, the sources said.

In November last year, the Beijing No. 2 Intermediate People's Court hand down the prison term to Dong. The trial was closed to the public.

The verdict named several individuals believed to be Japanese diplomats who were based in Beijing and acquainted with Dong, referring to them as "agents of an espionage organization" and identifying the Japanese embassy as such, according to the sources.

The journalist was detained in February 2022 after meeting with a Japanese embassy official in Beijing and was indicted in March 2023 for alleged espionage, the sources said.

The Japanese diplomat who met with Dong was temporarily detained while on duty, with China justifying its action by saying he had engaged in activities "inappropriate" for his embassy job.

Dong, known as a liberal commentator, is a longtime friend of former Japanese Ambassador to China Hideo Tarumi and was invited to his residence for a Lunar New Year celebration in early 2021, the Chinese journalist's family has said.

In the letter dated March 19 sent to Dong's family, Kanasugi claimed Japanese diplomats' activities in China are "justifiable," warning Sino-Japanese personnel exchanges could be "significantly impacted" if Chinese nationals were prevented from having contact with Japanese embassy officials, the sources said.

Since China's counterespionage law first came into force in 2014, 17 Japanese citizens have been detained for their alleged involvement in spying activities. Five remain in custody, according to Japan's Foreign Ministry.

The ambassador said Japan has asked China to enhance transparency in its implementation of the anti-espionage law, but "no progress" has been seen. He pledged in the letter to keep pressing Beijing to improve the situation, the sources said.

More than 60 people, including American journalist Bob Woodward and Tomoko Ako, a China studies professor at the University of Tokyo, have signed an open letter of concern over Dong's indictment, saying he faces a jail term for what they believe were "normal contacts with foreigners."

The former senior editor, who is not a Communist Party member, knows numerous Japanese and American journalists, scholars and diplomats. He was awarded fellowships at Harvard University and Keio University and was a visiting professor at Hokkaido University in Japan, according to Dong's family.