Vietnam has freed a high-profile blogger who has traveled to the United States, which is pressing for more such dissidents to be released.

"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 U.S. 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.

Tan, 47, a former policewoman, was arrested in 2011 for writing about human rights and corruption on her blog and sentenced to 10 years in prison on charges of spreading anti-state propaganda in a trial that also convicted fellow blogger Nguyen Van Hai, better known as Dieu Cay.

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.

"This release continues Vietnam's cynical practice of releasing high-profile dissidents from prison directly into forced exile, with immediate departure from the country being the price of their freedom," Phil Robertson, Asia deputy director at Human Rights Watch, said in a statement.

U.S. 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.