Activists called on US President Barack Obama to make human rights a central theme of his upcoming visit to Vietnam.
Obama should demand the release of political prisoners, as well as greater freedom of expression, the activist group ASEAN Parliamentarians for Human Rights (APHR) wrote in an open letter on Friday.
The 40-member group consists mainly of current and former lawmakers and campaigns against human rights violations in the region.
The US president was to arrive in Hanoi early Monday for a three-day visit ahead of next week's G7 summit in Japan. He will meet the leadership of Vietnam's communist one-party state, along with members of civil society and entrepreneurs.
The US-based Human Rights Watch (HRW) on Friday called on Obama to demand free elections in Vietnam.
He will arrive one day after parliamentary elections in Vietnam that will be tightly controlled by the Vietnam Communist Party.
"Obama should make it clear that the United States does not accept the idea that the Vietnamese people are not ready, willing and able to choose their own leaders," said Brad Adams, Asia director at HRW.