Undated photo of Canh Thong Do provided by a family member

A Vietnamese-born American citizen active in the Vietnamese democracy movement has been detained for more than three weeks in Ho Chi Minh City. The Vietnamese government reportedly suspects him of plotting terrorism, charges his family denies.

In early August, 47-year-old American Cong Thong Do was on vacation with his wife and son in Vietnam, visiting his mother-in-law. On August 14, police officers entered the house and asked Do and his wife to come in for questioning.

Do's son, Vien Dobui, says the police asked his mother about his father's connections with a controversial U.S.-based activist, Nguyen Huu Chanh, whom the Vietnamese government accuses of terrorism.

"In the meeting with the consulate, my father denied any ties with him or his party," he said.

But, using a pseudonym, Do has written articles on the Internet advocating multi-party democracy in Vietnam.

Unbeknownst to his family, Do had joined a political party called the People's Democratic Party of Vietnam.

The Vietnamese government and police have not publicly said what Do is accused of. His family has seen a letter from Vietnamese officials that says Do is suspected of terrorist activity.

And Do's wife, Jane Dobui, said police had shown her a handwritten letter accusing Do of plotting to bomb the U.S. Consulate in Ho Chi Minh City. The family says he has never advocated violence.

Do's family has not seen him since his arrest, but U.S. diplomats met with him on September 1.

"Members of the embassy staff have visited Mr. Do in custody, and we have not seen any evidence that Mr. Do was involved in violent activities," said Louis Lantner, an embassy spokesman in Hanoi.

Ho Chi Minh City lawyer Nguyen Van Dai, who is representing Do, says that Do said the police were questioning him about his relations with members of the People's Democratic Party in Vietnam.

Do's son, Dobui, says any accusations that his father had planned or advocated violence, especially against the U.S. government, are unfounded.

"They distribute and translate and publish articles on the Internet and they just try to get it out to as many people as possible. They are completely non-violent. On their Web site, they express their commitment to non-violence, to change through non-violent means," he said.

The Vietnamese anti-Communist scene comprises a number of small political parties, including the new Freedom and Democracy Party, and the People's Action Party of Vietnam, based in the United States. None of them have any broad political following in Vietnam.

Do's arrest stands in contrast to Vietnam's move last week to free several political prisoners. The United States had welcomed their release, particularly that of Internet dissident Pham Hong Son.