The American Secretary of State, John Kerry, has said the United States will continue to defend basic freedoms despite improving relations with the Communist leadership in Vietnam.
Speaking before talks in Hanoi with top leaders Mr Kerry said no-one should be punished for speaking their mind.
He said Vietnam would not reach its full potential or enjoy the fullest possible partnership with the US until it improved human rights.
“The United States recognises that only the Vietnamese people can determine their political system and we speak with some humility on these matters, because as you can read and see, we are working hard to perfect our own system,” he said.
“But there are basic principles we will defend: No one should be punished for speaking their mind so long as they are peaceful; and if trading goods flow freely between us, so should information and ideas. And we believe that progress in upholding these basic human rights will absolutely serve Vietnam’s interests.”
He said there would be no further relaxation of arms sales to Vietnam until the human rights situation improved.
Mr Kerry is visiting Vietnam to mark twenty years of diplomatic relations between the two countries.
He stressed that improved relations between them showed that old animosities could be put aside and that carried many lessons for a world threatened by conflict.
A veteran of the Vietnam war himself, he said the conflict that ended with the fall of Saigon 40 years ago was the result of the “most profound failure of diplomatic insight and political vision.”
He encouraged Vietnam to sign up for the Trans-Pacific trade pact, the TPP, currently being negotiated.
But he said Vietnam must uphold international standards itself if it wanted to benefit from the protection of international rules and regulations.
He emphasised that Washington would help Vietnam protect and control its territorial waters amid a continuing confrontation with China in the East China Sea.
The Obama administration partially lifted a ban on arms sales last year, allowing the sale of patrol craft and other equipment.
Vietnam wants a further relaxation of the ban and the finalisation of the TPP as it attempts to counter balance growing pressure from China.
Reporters Without Borders earlier urged the Secretary of State to raise the issue of freedom of information with Vietnamese leaders.
It said that Vietnam ranked 175th out 180 countries on the world press freedom index.
With some 30 bloggers still in jail, the organisation said the country remained the world’s biggest prison for journalists.
It urged the US to use the TPP negotiations to promote human rights and freedom of information in Vietnam in addition to demanding the right to form independent trade unions.
The Assistant Secretary of State responsible for promoting human rights and labour, Tom Malinowski, has been visiting Vietnam in advance of the visit by Mr Kerry.
He held a meeting with civil society activists in Hanoi, but reports said some government critics were detained in their homes in Ho Chi Minh City to prevent them meeting the visiting official.