"We welcome the decision by Vietnamese authorities to release Ta Phong Tan who decided to travel to the United States after her release from prison," said Terry White, a US Embassy public affairs officer.
"We remain deeply concerned for all persons imprisoned in Vietnam for exercising their human rights and fundamental freedoms and call on the government to release unconditionally all these prisoners and allow all Vietnamese to express their political views without fear of retribution," he said.
Over the past two years, several high-profile dissidents have been released and sent into exile in the United States, including Dieu Cay, who was released last October. His case had been mentioned by President Barack Obama.
Human Rights Watch welcomed Tan's release, but said no one should have been jailed for peacefully expressing their views.
US officials have said that Vietnam needs to improve its human rights record if it wants to expand economic, trade and military ties with the United States.
Hanoi says that no one is imprisoned in Vietnam for expressing their views, and that only law breakers are punished.
