The accusations of forced organ extraction were “ridiculous,” Huang Jiefu, a former deputy health minister who is in charge of overhauling China’s organ donation system, said in a speech. The Chinese government says that it switched from a system dependent on executed prisoners to one based on voluntary, nonprisoner donations on Jan. 1, 2015.

“I’m in stress,” Dr. Huang said of the accusations. “I couldn’t sleep well enough at night.”

“There is wild speculation” of “100,000 transplants per year from executed prisoners in China,” he added, possibly conflating the issues of using organs from prisoners convicted of capital crimes and organs from prisoners of conscience.

Some investigators and Falun Gong adherents say that their compiled data from individual hospitals shows at least 60,000 organ transplants a year, about six times the official total of about 10,000 last year, and that the difference is made up by forced organ extractions from prisoners of conscience.

In a cafe at the convention center, David Matas and David Kilgour, who first published a report on the issue in 2006, said they were familiar with the widespread skepticism, even hostility, not just from the Chinese government but from many outside China, including the news media. (An update to their book, “Bloody Harvest,” this time with Ethan Gutmann, author of “The Slaughter,” came out this year.)