Vietnam has released three of the four Vietnamese-born United States citizens it arrested in November and accused of involvement in terrorism. The release comes a day after the U.S. ambassador criticized the detentions. Matt Steinglass reports from Hanoi.

Leon Truong in Ho Chi Minh City,  just after his release by Vietnamese authorities, 11 Dec 2007

Vietnamese television reported Wednesday morning that Leon Truong had left Vietnam, bound for his home in the United States. Truong had been arrested in Ho Chi Minh City November 17 with five other activists from the Viet Tan party, a U.S.-based pro-democracy group.

Also released were Le Van Phan and his wife Nguyen Thi Thinh, arrested at Ho Chi Minh City's airport November 23 after a gun was allegedly found in their luggage. They were scheduled to return to the U.S. today.

The U.S. Embassy in Hanoi said Wednesday it welcomed the releases.

In a press conference Tuesday, U.S. Ambassador Michael Michalak had said that if the Americans were not released, the U.S. would protest.

U.S. Ambassador Michael Michalak during a news conference in Hanoi, 11 Dec 2007

Michalak expressed the view that the U.S. citizens had been detained for peaceful political activism, and questioned Vietnam's terrorism allegations.

"Vietnam has said that Viet Tan is on their list of terrorist organizations. Viet Tan is not on any list that I know of, of American terrorist organizations," he said.

One American Viet Tan member, Quoc Quan Nguyen, has not been released.

Vietnamese officials say, and a U.S. Embassy official acknowledged, that Nguyen had entered Vietnam using a forged Cambodian passport, complicating the charges against him.

The release of Phan and Thinh leaves unsolved the question of the gun they are alleged to have imported into Vietnam. Vietnamese press reports say the couple confessed to carrying the gun, but Michalak said Thinh had denied the charge.

The United States enjoys increasingly warm relations with Vietnam, and has been seeking Vietnamese cooperation on counter-terrorism efforts and on efforts to halt nuclear proliferation.