FILE - A Chinese Coast Guard vessel, with the disputed oil rig in the background, is seen in the South China Sea  June 13, 2014.
FILE - A Chinese Coast Guard vessel, with the disputed oil rig in the background, is seen in the South China Sea June 13, 2014.

WASHINGTON - The United States on Thursday partially lifted a long-time ban on lethal weapon sales to Vietnam to help it improve maritime security, a historic move that comes nearly 40 years after the end of the Vietnam War.

“The State Department has taken steps to allow for the future transfer of maritime security-related defense articles to Vietnam,” State Department spokeswoman Jen Psaki told a briefing.

State Department officials told a separate briefing that sales of any specific weapons would be evaluated on a case-by-case basis as requests came in from Vietnam.

They said the focus would be on helping Vietnam patrol and defend itself in the South China Sea, amid growing naval challenges from China, but said weapons sales could potentially include airborne systems as well as ships.

U.S. Senator John McCain, a former Navy pilot and prisoner of war in Vietnam, welcomed the deal.  But he's quoted as calling for improvements in the Hanoi government's human rights record.

The decision drew immediate fire from human rights groups worried that Washington could lose leverage over Vietnam.

“It's too soon; they haven't earned it,” said John Sifton, Asia advocate at the nonprofit group Human Rights Watch.

“They are still arresting people. The number of arrests and convictions has gone down from its peak in 2013, but ... the raw number of people going into the system is still larger than the number of people being released,” he said.

Vietnam's foreign minister last week said his country would welcome an end to the arms embargo after Reuters reported that Washington was nearing such a decision.

U.S. sources have said Washington could eventually sell Vietnam used U.S. P-3 Orion surveillance planes built by Lockheed Martin, which are being replaced by newer P-8A aircraft built by Boeing.

The State Department officials declined to name any specific weapons systems that could be under consideration or give a timetable for expected agreement on the first such deal. They said providing surplus U.S. defense equipment to Vietnam could trim the cost, but Vietnam would need to contribute as well.

“This is a very important first step that will engender future cooperation,” said one of the officials. “What this policy revision enables us to do is provide Vietnam the ability to defend itself in the context of its presence in the South China Sea.”

The officials said the decision follows some progress by Vietnam on human rights issues, including the release of six political prisoners and granting of amnesty for five more.

But they cautioned that further easing the arms embargo would require additional progress by Vietnam on human rights.

The officials said they did not expect any strong reaction from China since the focus would be on providing Vietnam with defensive systems.

“This is not an anti-China move,” said one of the officials.

The move to ease the arms embargo follows a gradual resumption of links between the United States and Vietnam over two decades, which has accelerated with a series of high-level diplomatic and military meetings in recent months.

U.S. industry executives see Vietnam as a promising market for their equipment given the U.S. military's strategic rebalance to the Asia-Pacific region.