"To date, we have received no formal notification of the charges against these individuals," Ambassador Michael Michalak told reporters at a media briefing.

"We have seen no information that would support the charges of terrorism against these individuals as suggested by the local media," he added.

Vietnamese authorities arrested U.S. citizens Nguyen Quoc Quan and Truong Van Ba on Nov. 17 and Nguyen Thi Thinh and Le Van Phan on Nov. 23.

Quan and Ba were among a group of six people detained in Ho Chi Minh City who were circulating leaflets for Viet Tan, a California-based pro-democracy group that the Vietnamese government considers a terrorist organization. Quan is a mathematician from Sacramento, and Ba is a community activist who lives in Honolulu.

Ba, whose Americanized name is Leon Truong, was released from jail Tuesday and has departed from Ho Chi Minh City's airport to the United States.

Vietnam state television showed Ba leaving jail and checking in at the airport.

Truong's daughter Lauren Truong says from Washington, D.C., she is very excited that her father is coming back home.

'NO EVIDENCE' OF TERRORISM

"We have seen no evidence that Viet Tan is a terrorist organization," Michalak said. "If there is evidence that this group is engaged in terrorist activities, I would like to see it."

The Vietnamese government has not announced formal charges against any of the detainees.

But according to Vietnamese media reports, authorities were investigating Quan and Ba for terrorism.

Thinh and Phan were detained after authorities allegedly found a weapon in their luggage when they arrived at the Ho Chi Minh City airport on Nov. 23, Vietnamese media reported.

A government spokesman has said they were detained for allegedly bringing arms into the country.

During her interview with U.S. Embassy officials, Thinh denied that there was a weapon in her luggage, Michalak said.

Viet Tan has said the two cases are unrelated and that Thinh and Phan have nothing to do with their group. Michalak said he has seen no evidence that shows the cases are linked.

Viet Tan says it promotes peaceful democratic change in Vietnam. The group says that the six people arrested in Ho Chi Minh City were circulating pamphlets promoting nonviolent political change.

"The United States will protest any actions taken to silence those engaged in the peaceful expression of political views," Michalak said.

Vietnamese government officials could not be reached Tuesday for comment on the cases.

Quan and Ba were detained along with four others, including two Vietnamese citizens, a French citizen and a Thai national, all of whom are still in custody.

4 MEMBERS OF INDEPENDENT TRADE UNION SENTENCED

Meanwhile, Vietnam sentenced four members of an independent trade union to up to 4.5 years in prison for defaming the Communist state, a court official said Tuesday.

The four were members of the United Workers-Farmers Organization of Vietnam, an unapproved union working on behalf of farmers whose land has been taken by the government for development.

Those sentenced were Doan Van Dien, Tran Thi Le Hong, Doan Huy Chuong and Phung Quang Quyen, court official Nguyen Minh Toan said.

The four were convicted of arranging or participating in interviews with foreign radio stations in which they accused the government of repressing strikes and arresting demonstrators, he said.