This aerial photo taken on January 2, 2017 shows a Chinese navy formation, including the aircraft carrier Liaoning (C), during military drills in the South China Sea.

A U.S. envoy on Monday denounced Chinese "intimidation" in the South China Sea at a meeting of Southeast Asian leaders, and conveyed an invitation from President Donald Trump for the leaders to attend a special summit in the United States.

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 reserve alone," U.S. envoy Robert O'Brien told the ASEAN-U.S. summit in a speech.

O'Brien, the White House national security adviser, read a message from Trump inviting the ASEAN leaders to "join me in the United States for a special summit" in the first quarter of 2020.