The Vietnamese government is preventing journalists from traveling to northwest Dien Bien province to look into reports of clashes between government troops and Hmong Christians.
Last week, international news reports said more than 3,000 Hmong had gathered in a mountainous district of Dien Bien province.
At the time, government officials were quoted as saying the Hmong gathered because they believed a "supernatural force" would take them to a "promised land" later this month. A Foreign Ministry statement also said some unidentified persons had tried to persuade the group to create a break-away Hmong kingdom.
Since then, there have been numerous reports that the military forcibly broke up the gathering.
The Center for Public Policy Analysis, a Washington-based human rights group that often represents Hmong causes, said more than 60 were killed and hundreds wounded during the crackdown.
There was no independent confirmation of the claim.
A report in official Vietnamese news media Sunday said that party representatives were sent to the area to persuade the Hmong to go home, and that some people had fallen ill because of unsanitary conditions at the remote location where they had gathered. The report said a child died from illness. The government says the situation in the area has now returned to normal.
The Vietnamese government has repeatedly turned down journalists' requests to go to the area.
The U.S. Embassy in Hanoi said it is aware of the reported clashes and was trying to verify what happened. An embassy spokesman said the U.S. had urged both the security forces and the Hmong to use restraint.
The Hmong are among several small ethnic groups that live in the border regions of China, Vietnam, Laos and Thailand. Many Hmong in Vietnam are Christians, although the country is officially atheist, and more Vietnamese follow Buddhist traditions.
Many Hmong were allied with the United States during its war in Vietnam. That earned them the enmity of the Vietnamese Communist Party, which took control of the country in 1975.
At the time, hundreds of thousands of Hmong fled the country. Some inside the country and overseas Hmong advocacy groups say those still in Vietnam face official discrimination and abuses. Vietnam has seen dramatic economic growth in recent years, which has lifted millions of people out of poverty. However, the United Nations' country chief says many areas with ethnic minority populations remain impoverished.