WASHINGTON, Dec. 21 (Xinhua) -- Chinese Ambassador to the United States Cui Tiankai has extended his deepest condolences to the family of Ezra Vogel, a renowned sinologist who died at the age of 90 on Sunday.

"So sad to learn (about) the passing of Professor Ezra Vogel. He was an outstanding scholar on China and an old friend of the Chinese people," Cui tweeted hours after the Fairbank Center of Chinese Studies at Harvard University, where Vogel served as professor emeritus, announced the news.

"Throughout his lifetime he was dedicated to greater mutual understanding between the Chinese and American people and made significant contributions to their friendship and China-U.S. relations," said Cui. "His wisdom and insight on China have been of immeasurable value not only to people in the field of study, but also to the world."

"I have known Professor Vogel for a long time and learned a great deal from him. I believe his ideas and commitment will always have an impact on us. My deepest condolences to Professor Vogel's family," he said.

Vogel was one of the leading scholars on modern Japan and China. His monographs on China, including "Deng Xiaoping and the Transformation of China," a 900-page book published in 2011, provide insightful analysis and help Westerners better understand the country.

Vogel, together with dozens of other experts and former senior U.S. officials, released a joint statement in April, urging the United States to cooperate with China to combat the COVID-19 pandemic.

In July 2019, he co-authored an open letter entitled "China is not an enemy" to the U.S. president and Congress, in which more than 100 American academics, foreign policy experts, military and business leaders called on the Trump administration to re-examine its views on and approach to China.