WASHINGTON (Reuters) - White House national security adviser Robert O’Brien is on his way to Vietnam and the Philippines, countries that share U.S. concern over China’s increasingly assertive behavior and extensive maritime claims in Asia, the White House said on Wednesday. Tweets from the White House National Security Council said O’Brien would meet leaders in both countries “to reaffirm the strength of our bilateral relationships and to discuss regional security cooperation.” O’Brien’s trip follows a visit to Hanoi last month by U.S. Secretary of State Mike Pompeo. That visit came a week after Vietnam freed a Vietnamese-born U.S. citizen, Michael Nguyen, who had been sentenced to 12 years in prison for “attempting to overthrow the state.” The former Vietnam War foes now have warm relations in spite of U.S. concerns about Hanoi’s human rights practices. Washington also has concerns about human rights in the Philippines, where President Rodrigo Duterte has been engaged in a war on drugs in which thousands of urban poor have been killed, many in mysterious circumstances. On a visit last year, Pompeo assured the Philippines that Washington would come to its defense if it came under attack in the South China Sea, where Manila has competing claims with China and other countries, including Vietnam.