A prominent Vietnamese author who campaigns for press freedom and civil rights has been arrested, authorities said Wednesday, hours after annual human rights discussions between the United States and Vietnam.

Pham Doan Trang, who has pushed for change on a host of controversial issues including land grabs and LGBT rights, was picked up Tuesday from her rented home in Ho Chi Minh City and detained on anti-state charges.

The writer, who had spent years working as a journalist for state media, was accused of "making, hoarding and disseminating information... against the Socialist Republic of Vietnam", the ministry of public security said.

Vietnam's authoritarian government has been accused of stepping up the persecution of critics ahead of a leadership transition at the apex of the ruling Communist Party.

"Opposing the state" is punishable by up to 20 years jail.

The arrest came shortly after an annual human rights dialogue between Washington and Hanoi.

In the past, Trang claimed she was beaten and detained by police over her work.

Last year she said police harassment and the alleged abduction and abuse of colleagues had forced her to withdraw from an independent publisher of political books that she helped set up.

In a letter she wrote around that time -- entitled "Just in case I am imprisoned" -- she urged the public to focus on fighting for free and fair elections in Vietnam, rather than her freedom.

"I don't want freedom for just myself: that's too easy," she wrote.

"I want something greater: freedom for Vietnam."

Human Rights Watch demanded her immediate release, calling the arrest "a grave injustice".

The rights group said Trang stood out for her determination to attract international attention to Vietnam's abysmal human rights record.

In 2016, police detained her while on her way to a meeting with US President Barack Obama who had invited her to join a gathering of activists during his visit to Hanoi.

Trang, who has also spoken out over forced confessions and corporal punishment in Vietnam, won an award in 2019 from press watchdog Reporters Without Borders for her work on press freedom.

According to the Committee to Protect Journalists' tally Trang is the fourth writer facing anti-state charges in Vietnam this year.

© AFP