Updated

A Vietnamese-American pro-democracy activist has been arrested and accused of terrorism for allegedly trying to sabotage liberation celebrations commemorating the end of the Vietnam War, state media said Sunday.

Nguyen Quoc Quan, 58, of California, was detained April 17 after arriving at the airport in southern Ho Chi Minh City, Tuoi Tre newspaper reported. He is accused of planning to hold protests for Viet Tan, a banned U.S. exile group, during this week's May Day festivities and the April 30 anniversary of the fall of the former U.S.-backed South Vietnamese capital, Saigon, to the northern communists in 1975.

Authorities also found many documents in Quan's possession on "terrorist training," the paper said. Quan, a mathematician, was previously sentenced to six months in jail by a Ho Chi Minh City court in 2008 for terrorism.

After being deported from Vietnam, Quan continued to travel from the U.S. to Thailand and Malaysia to train members of the Viet Tan group on nonviolent struggles in Vietnam, Tuoi Tre said.

Hanoi often uses vague national security laws to charge pro-democracy activists with terrorism, but the U.S. government has said it has seen no evidence that California-based Viet Tan, also known as the Vietnam Reform Party, is a terrorist organization.

"The Vietnamese government's accusation of 'terrorism' against Dr. Quan is completely fabricated and has no basis," said a statement posted on Viet Tan's website. "The detention of Dr. Nguyen Quoc Quan is the latest example of the Vietnamese Communist Party's ongoing crackdown on human rights defenders."

Meanwhile, the Capital Security newspaper reported that authorities have released activist Bui Thi Minh Hang, 48, from a re-education camp near Hanoi.

She was taken there in November for causing social disturbances after playing an active role in the unprecedented protests against China last summer over tensions surrounding disputed territory in the South China Sea.

The U.S. Embassy and rights groups had called for her release. The newspaper said she was freed as part of the government's policy of leniency on the occasion of the celebrations surrounding the fall of Saigon and May Day.