China has made sweeping maritime claims in the resource-rich waters of the South China Sea, and angered neighbors by sending ships into the busy waterway, where several members of the Association of Southeast Asian Nations (ASEAN) also have claims.

"Beijing has used intimidation to try to stop ASEAN nations from exploiting the off-shore resources, blocking access to 2.5 trillion dollars of oil and gas reserves alone," U.S. envoy Robert O’Brien told the ASEAN-U.S. summit in a speech. 

O'Brien expressed his support for the role of ASEAN countries.

"The region has no interest in a new imperial era where a big country can rule others on a theory that might makes right," added O’Brien, the White House national security adviser.

He also read a message from Trump inviting the ASEAN leaders to "join me in the United States for a special summit, meeting at a time of mutual convenience in the first quarter of 2020."

Trump has skipped the ASEAN-U.S. summit for the past two years, sending Vice President Mike Pence in 2018.

At this year’s summit, U.S. Commerce Secretary Wilbur Ross was the highest-ranking delegation official, prompting the 10-member ASEAN to downgrade the summit to a "troika" attended only by top leaders from Thailand, Vietnam and Laos.

Vietnam's Foreign Minister Pham Binh Minh (R) meets with Robert O’Brien,
the White House national security adviser, at the 35th ASEAN Summit
in Bangkok,Thailand, November 4, 2019. Photo by Vietnam News Agency.

During the summit, O'Brien also met with Vietnam's Deputy Prime Minister and Foreign Minister Pham Binh Minh, affirming the U.S.'s support for freedom of navigation and overflight in the South China Sea, the Ministry's Foreign Affairs said in a statement.

Vietnam calls the waters the East Sea.

The two officials agreed to work together to further promote bilateral relations in 2020, when the two countries celebrated the 25th anniversary of normalization of the Vietnam-U.S. relations and Vietnam assuming the chairmanship of ASEAN 2020, and becoming non-permanent member of the United Nations Security Council.