Chinese observers said the move is designed to enhance ties as Vietnam seeks more international support to guard its interests in the South China Sea while the United States expands its presence in the Asia-Pacific region in line with its strategic pivot to Asia.

　　Sang is only the second head of state from Vietnam to visit Washington since relations were normalized in 1995. Former Vietnamese president Nguyen Minh Triet was the first, visiting the US in 2007.

　　The two leaders discussed a global trade pact called the Trans-Pacific Partnership that aims to create a vast free trade collective. Twelve nations covering 40 percent of the world economy are taking part in the pact, including Vietnam and most recently Japan.

　　At the meeting, Obama spoke of the "steady progression and strengthening" of bilateral ties and the " extraordinarily complex history" between the two countries. He called Truong's visit a move that "signifies the maturing and the next stage of the development between the United States and Vietnam".

　　The two presidents also discussed maritime issues in the South China Sea.

　　Qi Jianguo, former Chinese ambassador to Vietnam, said Sang's visit shows the two countries are strengthening relations. High-ranking officials from both sides rarely make visits to each nation, Qi said.

　　"Before visiting Washington, the Vietnam leader also paid visits to other big powers including China and Russia, so the Washington visit shows the diplomatic balance that Vietnam hopes to reach in its foreign policy," he said.

　　Li Guoqiang, deputy director of the Center for Chinese Borderland History and Geography at the Chinese Academy of Social Sciences, said both Washington and Hanoi want to enhance ties.

　　"Hanoi not only seeks ways to resolve the South China Sea issue with China, but hopes to strengthen its maritime power with the support of powers outside the region," Li said.

　　Washington aims to become more deeply involved in South China Sea territorial issues in order to help contain China and maintain dominance in the region, he added.

　　During the meeting with Sang, Obama said he "very much" appreciated Vietnam's commitment to working with the Association of Southeast Asian Nations and the East Asia Summit to establish a code of conduct to resolve issues "peacefully and fairly".

　　Although the US said it remains neutral on territorial disputes related to the South China Sea, its rhetoric on the issue has sounded alarms in China, Li said.

　　"It is hard for the US to get away with the more and more complicated situation in the South China Sea," he added.

　　Obama has focused more heavily on Southeast Asia in recent years and sees it as a region with large economic potential that has been neglected by US policymakers in the past.

　　Sang is the fourth Southeast Asian leader to visit the White House this year.

　　Xinhua and AFP contributed to this story.