In recent months, the U.S. military has stepped up its freedom of navigation operations in the region.
South China Sea
On Friday an American warship approached the Paracel Islands, an island chain claimed by Beijing in the South China Sea.
All ten members of the Association of Southeast Asian Nations will take part in the first Asean-US Maritime Exercise.
The USS Wayne E. Meyer sailed within 12 nautical miles of Fiery Cross and Mischief Reefs in the South China Sea.
The U.S. Navy flew a small group of Philippine generals, officials and journalists to the aircraft carrier Ronald Reagan.
China is holding exercises near Taiwan, days after a paper said Beijing would not rule out retaking the island by force.
China demanded that the United States "immediately cancel" a potential sale of $2.2 billion in arms to self-ruled Taiwan.
China strongly objects to naval activity by other nations in the South China Sea.
Shanahan said he can't ignore the communist giant's military development on the manmade outposts.
Acting Defense Secretary Patrick Shanahan arrived Wednesday in Asia on a high-profile weeklong trip.