Police arrested the activists while they were meeting in Ho Chi Minh City on Saturday, according to Viet Tan, a California-based group that says it has members around the world and underground in Vietnam .
U.S. Embassy officials confirmed that a U.S. citizen was arrested over the weekend but released no further details. They are requesting an interview with him and investigating the reasons for his arrest.
"The United States will protest any actions taken to silence those engaged in the peaceful expression of political views," a statement from the embassy said.
The two U.S. citizens and the French citizen were members of Viet Tan, a statement released by the organization said. The other three detainees were a Thai and two Vietnamese, the group said.
Vietnamese authorities would not immediately comment, and French and Thai officials could not be reached.
According to Viet Tan, among those detained were Nguyen Quoc Quan, a mathematician from Sacramento, California; Truong Van Ba of Honolulu, Hawaii; Nguyen Thi Thanh Van, a journalist from Paris, France; and Somsak Khunmi, from Ubon, Thailand.
The detainees were having a discussion with other activists about promoting peaceful democratic change before security police arrested them at a private residence in Ho Chi Minh City, according to Viet Tan.