The U.S. ambassador to China, Clark Randt, says he hopes Chinese authorities will soon release Jude Shao, an American businessman serving a 16-year prison sentence for alleged tax fraud.

The U.S. ambassador traveled to Shanghai Friday, after Chinese authorities granted him permission to visit American Jude Shao. He has been jailed since 1998 on allegations that he engaged in tax fraud related to his medical equipment export business.

Shortly after visiting Mr. Shao in prison, Ambassador Clark Randt issued a statement saying he is "very hopeful" that Chinese authorities will release the businessman soon on medical parole. Mr. Shao's family says he is suffering from a heart condition, and has complained of meager food rations in prison.

Mr. Shao's friends and business associates in the United States have organized an effort to push for his release. On their Internet site, they say police arrested Mr. Shao after he refused to comply with Chinese agents, who demanded bribes from him.

They say he was kept incommunicado for more than two years before he was sentenced.

Human rights advocates call the sentence excessive, and question the legality of his arrest. Nicholas Becquelin of the Human Rights in China group in Hong Kong says the U.S. call for his release on medical grounds may give the Chinese authorities a chance to neutralize allegations that this is an infringement of human rights, this time involving a foreign investor.

"There can only be a diplomatic and political solution to the case, and one that allows the Chinese government and the courts not to lose face, and not to admit that they made a mistake, or that the person was prosecuted with other motives than just tax evasion," said Nicholas Becquelin. "It's a bit of a bargain[ing] chip in the larger diplomatic relations."

U.S. consular officials have regularly checked on Mr. Shao. However, the visit by the ambassador underscored the importance that the United States government has given to his case, which has prompted inquiries from members of Congress.

Officials with China's Foreign Ministry on Friday said they had "taken notice" of Mr. Randt's visit to the prison Friday.