It is "crucial" for Vietnam to reaffirm "its commitments to reform including good governance, the rule of law and human rights", visiting European Council President Herman Van Rompuy said in a press briefing with Vietnam's leader Truong Tan Sang in Hanoi.

The normally uncontroversial Belgian added that he still retained faith in the "future of Vietnam".

The US embassy in Hanoi on Tuesday also condemned the country's muffling of freedom of expression, hours after two musicians joined dozens of other dissidents behind bars.

On Tuesday a court in the southern business hub of Ho Chi Minh City jailed musicians Viet Khang, 34, for four years and Tran Vu Anh Binh, 37, for six years after finding them guilty of "anti-state propaganda".

"The Vietnamese government should release these musicians, all prisoners of conscience and adhere to its international obligations immediately," said embassy spokesman Christopher Hodges.

The jailed duo, who will also serve a two-year house arrest after their release, are known for penning lyrics condemning police action against anti-China activists and the imprisonment of dissidents.

On Tuesday, New York-based Human Rights Watch urged Van Rompuy publicly to press Vietnam to release all political prisoners and detainees during his three-day visit to the tightly-controlled county.

"Vietnam regularly imprisons its citizens for asking for democracy and the same freedoms that Europeans take for granted," said Brad Adams, Asia director at Human Right Watch.

"Van Rompuy has an ethical obligation to make clear to the Vietnamese government that it cannot operate a repressive dictatorship."

Agence France Presse - November 1st, 2012