Jennifer Truong, the last of the three to be held, will leave the country on Thursday, Nguyen Phuong Nga, spokeswoman for the Ministry of Foreign Affairs, told reporters.

She said they were detained "for inciting others to provoke public insecurity".

"After taking these cases into consideration, with the clemency policy of Vietnam and in accordance with Vietnamese law, the authorities... decided to deport these three people," she said.

US-based group Viet Tan (Vietnam Reform Party) said the trio, who are all of Vietnamese descent, had been held since a March 14 demonstration in Ho Chi Minh City against government corruption and illegal land expropriation.

It earlier said Nguyen Quang Khanh was released Wednesday, while Nguyen Ly Trong was returned to the US earlier this week.

In Washington, a State Department spokesman said on Tuesday that US diplomats had been informed by Vietnam that Americans were detained.

Authorities are also holding a French-Vietnamese citizen, Pham Minh Hoang, who was accused in September of being a Viet Tan member and of plotting to overthrow the government.

Nga could not immediately comment when asked about the case of Hoang, a university lecturer.

Vietnam is a one-party communist state that labels Viet Tan a "terrorist organisation".

Agence France Presse -March 24, 2011