HANOI - US Secretary of State John Kerry on Friday hailed the "remarkable transformation" of relations with Vietnam 20 years after ties were established, but warned Hanoi's poor rights record stood in the way of deeper bonds between the former wartime foes.
Kerry, on the last leg of a trip through the Middle East and Asia, is in Hanoi to mark the diplomatic milestone with the communist nation and hold talks on trade, human rights and regional security - including maritime issues in the contested South China Sea.
The top US diplomat met President Truong Tan Sang early Friday at the French colonial-era Presidential Palace, shaking hands with the official in front of a giant bust of Vietnam's independence hero Ho Chi Minh.
The two nations "have again proven that former adversaries really can become partners," Kerry said in a speech.
But progress on human rights is essential for "a deeper and more sustainable" partnership between the countries, which fought a bitter decades-long war which ended in 1975.
"Only you can decide the pace and direction of this progress. But I'm sure you've noticed that America's closest partnerships in the world are with countries that share a commitment to certain values," Kerry added.
From an eight-fold increase in US visitors to Vietnam, to a twenty-fold rise in the number of Vietnamese students studying in the US, the former enemies have come a long way in 20 years, he said.
Bilateral trade has surged from around $450 million in 1995 to more than $36 billion today, even as the two countries work towards concluding the ambitious US-led Trans-Pacific Partnership (TPP) trade deal.
"These aren't just statistics. They're a measure of one of the most remarkable transformations in the history of world affairs," Kerry said.
But he cautioned that authoritarian Vietnam needs to improve its patchy rights record.
"Millions of people in Vietnam are already freely expressing themselves on Facebook," Kerry said, adding that protecting free speech would "strengthen social cohesion and stability".
The one-time presidential hopeful has said his political activism was inspired by his experiences patrolling waterways in the Mekong Delta on Swift Boats during the Vietnam War.
He served with the US Navy from 1966 to 1970 as a naval lieutenant and it was on his return after two tours of duty that he became a fierce campaigner against the war, which ended in 1975.
- Trade and human rights -
Later Friday, Kerry is scheduled to hold talks with Vietnam's Foreign Minister Pham Binh Minh, covering regional security and economic ties - including the TPP.
Labour rights issues - Vietnam does not allow independent trade unions - have been a sticking point in the ongoing trade negotiations, which also include Singapore, Malaysia, Japan and other Pacific Rim countries, but not China.
Kerry said this week in Singapore that the TPP, a key economic priority for the US administration, was close to completion after years of painstaking talks.
In a sign of the warming ties with Hanoi, last year Washington partially lifted a 40-year ban on arms sales to Vietnam.
In January, US Defense Secretary Ashton Carter pledged $18 million to help Vietnam buy US-made coastguard patrol boats.
But the easing of the ban - which was in place since the end of the Vietnam War in 1975 - "is the limit thus far of our efforts along those lines", a senior US state department official told reporters travelling with Kerry.
Vietnam's intolerance of domestic dissent has also limited US efforts to assist the communist nation in bolstering its maritime capabilities.
Hanoi is locked in a longstanding territorial dispute with Beijing over island chains in the South China Sea, which is a key global shipping route and a major geo-strategic tension point between China and the US.
Speaking in Malaysia Thursday, America's top diplomat said his country "will not accept" curbs on "freedom of navigation and overflight" of the sea.
On Friday, Kerry said resolution of disputes in the South China Sea "should depend on who has the better argument not who has the bigger army", and urged all parties to refrain from "provocative acts" in the contested waters.