US President Barack Obama (R) and Vietnamese General Secretary Nguyen Phu Trong shake hands during a meeting in the Oval Office of the White House in Washington, DC, July 7, 2015
US President Barack Obama welcomed the leader of Vietnam's Communist Party on Tuesday to the White House for historic but "candid" talks marking two decades of rapprochement between the former enemies.
Nguyen Phu Trong is the first general secretary of the Vietnamese Communist Party to visit the United States and the White House, and was given the rare honor of an Oval Office meeting -- usually reserved for heads of state and government.
Washington and Hanoi -- which ended their bitter war 40 years ago, and are marking the 20th anniversary of the formal normalization of relations -- are seeking stronger ties in the face of an increasingly assertive China.
The two men, smiling and rather relaxed as they sat next to each other in the Oval Office after their highly symbolic talks, insisted on the progress made in the last two decades.
"Obviously there has been a difficult history," Obama said. "What we've seen is the emergence of a constructive relationship that is based on mutual respect."
The US president said trade ties, tensions in the South China Sea over Beijing's territorial claims and the thorny issue of human rights had been raised.
"We discussed candidly some of our differences around issues of human rights," Obama said, expressing confidence that any "tensions can be resolved in an effective fashion.
Trong described the talks as "cordial, constructive, positive and frank," and also qualified their talks on trade and rights as "candid."
Without explicitly referring to China, he raised concerns about recent activities in the South China Sea "that are not in accordance with international law."
Beijing has taken a more assertive stance on territorial claims in the South China Sea -- including deploying military equipment to the disputed Spratly Islands, claimed in part by Vietnam.
The South China Sea is home to strategically vital shipping lanes and is believed to be rich in oil and gas.
Obama -- who leaves office in 18 months -- said he looked forward to visiting Vietnam "sometime in the future," without offering a specific timetable.
- 'Nothing but promise' -
The White House talks -- followed by a lunch hosted by Vice President Joe Biden, who said the future held "nothing but promise" for US-Vietnam ties -- have certainly sparked criticism.
A few hundred protesters rallied outside the White House, calling for expanded human rights in Vietnam -- an issue that has sparked concern among some American lawmakers about deepening ties.
Demonstrators carried signs with slogans like "Freedom of speech in Vietnam now" and called on Hanoi to release all political prisoners.
In an open letter to the president, nine Democratic and Republican members of Congress have complained that the invitation and warm welcome for Trong send the wrong message.
"This authoritarian one-party system is the root cause of the deplorable human rights situation in Vietnam," the letter said, calling for Obama to demand the release of Vietnamese political prisoners.
Beyond the rights question, another major issue on the table is trade. Obama is seeking to reach a 12-nation Pacific trade pact, known as the Trans-Pacific Partnership, that would include Vietnam.
Republican Congressman Chris Smith, one of those who signed the letter, and others in Congress would like to see Vietnam excluded from the TPP until it makes progress on political rights.
"President Obama... still believes that trade will change Vietnam's behavior," Smith told AFP ahead of the visit.
"After Vietnam was given admission to the World Trade Organization in 2007, it ratcheted up repression; expecting a different result now is just plain unrealistic."
- 'Astounding' progress -
John Sifton, an Asia specialist for Human Rights Watch, told AFP that not enough had changed in Vietnam to warrant an Oval Office sit-down.
He called on Obama "to raise the volume on the human rights concerns -- especially so if the two countries are planning to announce a new level in their diplomatic ties."
Part of taking it to the next level could be the lifting of a US ban on weapons sales, which Vietnam is keen to achieve.
In October, Washington announced the partial lifting of the ban, and authorized sales of maritime defense equipment to Vietnam. But current US laws bar the sale of lethal weapons to Hanoi.
The State Department official said that Washington wanted to see more progress on human rights before going any further.
On Wednesday, Trong was to meet with Senator John McCain, a onetime prisoner of war in Vietnam who hailed the "astounding" progress made in bilateral ties and called for further easing of the lethal weapons ban.