BEIJING — An ethnic Mongolian dissident who completed a 15-year prison sentence last week for political crimes has been confined to a luxury hotel in Inner Mongolia along with his wife and son, according to a family member who spoke with the police earlier this week.

The dissident, Hada, has been missing since last Friday, when he was reportedly released from the detention center where he served his time for espionage and “splitting the nation.” A day later, photographs were anonymously published on the Internet showing Mr. Hada and his family sharing a meal together and wanly toasting the camera.

Like many ethnic Mongolians, Mr. Hada, his wife and their son use one name.

Human rights advocates have expressed concern that the authorities have summarily extended Mr. Hada’s punishment by preventing his return to Hohhot, the provincial capital of Inner Mongolia, which is officially known as an autonomous region.

“The Chinese authorities must immediately clarify Hada and his wife and son’s current status and whereabouts,” Catherine Baber, deputy director of Amnesty International, said in a statement Wednesday. “They cannot simply hide people they find embarrassing or inconvenient.”

It appears that the authorities are doing just that. According to Mr. Hada’s sister-in-law, Naraa, a high-ranking police official summoned her to the Public Security Bureau on Tuesday and explained that the family was staying at an unidentified five-star hotel “for their own good.” She said the official would not reveal the name of the hotel or set a limit on how long Mr. Hada and his family would be held.

“They are afraid Hada’s remarks might put him in trouble again, so they are just giving them some quiet time,” Ms. Naraa said in a telephone interview Wednesday evening.

The official, she added, acknowledged that the photographs that appeared online last weekend were taken and disseminated by the police.

Mr. Hada, 55, is considered something of a hero among the region’s six million ethnic Mongolians, many of whom have long complained about the dilution of their language and culture by a population that is 80 percent Han Chinese.

A writer and owner of a popular Mongolian-language bookstore in Hohhot, Mr. Hada was arrested in 1995 after organizing a rally in which some protestors demanded more autonomy for Inner Mongolia while others, more radically, called for independence. His conviction a year later was partly based on his role as an organizer of the Southern Mongolian Democracy Alliance, an illegal group that called for a public referendum on the region’s future.

The espionage charge stemmed from interviews Mr. Hada gave to overseas journalists and the Voice of America.