In China under President Xi Jinping, journalists who stray from the Communist Party’s official line are increasingly being muzzled as part of a widespread crackdown on civil society that has led to human rights lawyers and feminists being imprisoned, influential bloggers having their social media accounts deleted and professors being told to limit the use of foreign textbooks.

In Mr. Yang’s case, he may have fallen victim to new rules on what retired Communist Party cadres can say, and specifying that their public opinions must have “a high level of consistency with the Party Central under comrade General Secretary Xi Jinping.” As a senior reporter for China’s government-owned official news service for many decades, Mr. Yang was a longtime party member. But he has also been highly critical of the government, dealing a devastating blow to the official account of the famine and Mao’s legacy in his book, and speaking out in public forums around the world.

Until now, he was allowed to travel internationally to receive accolades for his work. Last year, Mr. Yang went to Sweden to receive the Stieg Larsson prize, an award established in memory of the crime writer and journalist, who died in 2004, and given to people working in his spirit. In 2013, he traveled to the United States to receive the Manhattan Institute’s Hayek Prize, named after the economist and philosopher Friedrich Hayek. There, he delivered a scathing indictment of modern China under the Communists, who he said had created a society in which “only the already powerful can acquire wealth.”

“China’s path to harmony and stability is to reject this system and instead to heed Hayek’s call to avoid government coercion, respect individual freedom and allow further economic and political liberalization,” Mr. Yang said.

Although Mr. Yang said on Tuesday that he had his passport, leaving the country against the wishes of Xinhua, a powerful arm of the government and Communist Party, might jeopardize any plans he might have to publish future works. Calls during working hours to Xinhua’s main office in Beijing went unanswered.