US deputy secretary of state John Negroponte, on a visit to Vietnam, has lauded the "close partnership" between the two countries.

He praised Vietnam's "economic miracle" and its good will toward its former foe, but also called for more political and legal freedoms.

Mr Negroponte is visiting Vietnam for the first time since he was part of US forces in the Vietnam War in 1973.

His visit comes at a time of rising tensions in the South China Sea.

China and Vietnam each claim territory in the area, believed to hold major oil and gas resources.

"It's clear his visit will result in closer ties between the US and Vietnam," Carl Thayer, a Vietnam expert, told the BBC.

"I cannot believe that strategic matters are not being discussed," said Mr Thayer, who is a visiting fellow at the Strategic and Defence Studies Centre at the Australian National University in Canberra.

Warming ties

"I'm very optimistic about the future of our relationship," Mr Negroponte said during a news briefing in Hanoi on Friday morning, The Associated Press reported.

Even though the two sides fought a "bitter and difficult" war, "on both sides, there seems to be a tremendous amount of good will", he was reported to have said.

He praised Vietnam's economic growth, which has averaged about 7% a year over the last decade, but he also said he had raised the issue of human rights in all his meetings.

Mr Negroponte had been due to visit Vietnam last year but this was postponed for reasons that are still unclear.

His trip comes two years after that of US President George Bush and Secretary of State Condoleezza Rice, and follows the visit of Vietnamese Prime Minister Nguyen Tan Dung to Washington in June.

Those trips helped to produce a blueprint for closer ties, particularly in education, science and technology, with new US funding offered for scholarships.

Vietnamese news reports quoted Prime Minister Dung expressing appreciation for agreements to work closer on investment, trade, and environmental protection.

Mr Negroponte's schedule has included a meeting with Mr Dung on Thursday, and meetings with the ministers for education, defence, and foreign affairs. He is to visit Ho Chi Minh City (formerly Saigon) to meet business leaders on Saturday before going on to Cambodia.

Regional pressures

The trip has a broader significance in the Asia-Pacific, analysts believe.

Territorial tensions have risen in recent months between Vietnam and China, over disputed areas of the South China Sea, where major US and other oil companies are hoping to extract oil and gas.

"No matter what the US does, there will always be speculation - and that suits both Vietnam and the US," said Mr Thayer.

He explained that Vietnam needs the good will of both China and the US, to balance trade and security concerns.

"Mr Negroponte's trips could help give the US an enhanced leadership role in the region, as well as closer bilateral ties. And it allows Vietnam to show the region that it is not isolated with regard to China," said Mr Thayer.

Two days before Mr Negroponte's arrival in Hanoi, an Internet writer and activist was sentenced to 30 months in prison for tax fraud.

Nguyen Hoang Hai, whose pen-name is Dieu Cay, had criticised his government's handling of disputes with China over the Spratley and Paracel Islands in the South China Sea.

His imprisonment was condemned by Human Rights Watch as part of a broader crackdown on democracy activists in Vietnam.

Analysts also see his treatment as indicative of the sensitivity surrounding Vietnam's ties with China.

"Vietnam wants to deal with China privately," Mr Thayer said.

US support could help Vietnam focus more on economic growth, however, with new investments expected to emerge after this trip.