Just four months ago, China’s defense minister, Gen. Li Shangfu, was at a forum for regional officials in Singapore, serving as the face of his country’s bold vision for reshaping Asia’s balance of power. He cast China as a force for stability and accused the United States of stirring trouble in the region, suggesting that its leaders should “mind your own business.”

Now, General Li has been dismissed after nearly two months out of public view — the latest example of China’s capricious rules of power under the strongman leader Xi Jinping.

China’s announcement on Tuesday ended some uncertainty about General Li’s professional fate but leaves open questions about whether he is being investigated for any offenses. Officials in the United States had earlier said that Chinese authorities had placed him under investigation for corruption.

General Li is the second Chinese minister to be purged this year without explanation and under a cloud of suspicion; the foreign minister, Qin Gang, was dismissed in July. The general’s removal also followed an abrupt shake-up in the leadership of China’s nuclear force, the highest-level upheaval in China’s military in recent years.

General Li’s removal from his post was announced by Chinese state media in brief reports that noted other official appointments and dismissals. The reports said the decision was made on Tuesday at the end of a meeting of the Standing Committee of China’s National People’s Congress — a council in the country’s Communist Party-controlled legislature that formally appoints senior government officials.

General Li was last seen in public in late August, when he spoke at a forum in Beijing attended by officials from African nations.

For much of his career, General Li was involved in China’s space and rocket programs, developing missiles and other advanced weapons — a part of his résumé that has been the subject of scrutiny since the reports emerged about the potential corruption probe.

In late July, Mr. Xi abruptly replaced the two top commanders of the Rocket Force, the arm of the Chinese military that oversees its nuclear missiles and much larger array of conventional missiles. The Chinese government gave no explanation for their ousting, but news reports in Hong Kong have linked the upheaval to a probe into corruption or other misconduct in the Rocket Force, which Mr. Xi created in late 2015.

General Li was under U.S. sanctions for his role in buying Russian fighter planes and missiles, and China rejected calls from the United States for talks between General Li and his American counterpart unless Washington lifted the penalties.

Amy Chang Chien contributed reporting from Taipei.