The drills around Guam and Tinian may also get the attention of nearby North Korea. Tensions between the US and North Korea spiked last month after Pyongyang launched a ballistic missile and the US sent an aircraft carrier strike group to the region.
The drills, which are led by France and include the United Kingdom, will practice amphibious landings, delivering forces by helicopter and urban patrols.
"The message we want to send is that we're always ready to train and we're always ready for the next crisis and humanitarian disaster wherever that may be," said U.S. Marine Corps Lt. Col Kemper Jones, the commander of the 3rd Battalion, 8th Marine Regiment. About 100 Marines from Jones' unit will be part of the drills slated for this weekend and next week.
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Critics fear China's actions could restrict movement in a key waterway for world trade and rich fishing grounds.
China says its island construction is mainly for civilian purposes, particularly to increase safety for ships. It has said it won't interfere with freedom of navigation or overflight, although questions remain on whether that includes military ships and aircraft.
"A reminder in this exercise is that lots of other countries besides the United States have an interest in that international order," said Rapp-Hooper, who is a senior fellow with the center's Asia-Pacific Security Program.
The exercises come amid modestly growing European interest in the South China Sea, said David Santoro, a senior fellow for nuclear policy at Pacific Forum CSIS, a Honolulu think tank.
Japan, which is sending 50 soldiers and 160 sailors and landing craft, has been investing in amphibious training so it can defend its own islands. Tokyo is particularly concerned China might attempt to take over rocky, uninhabited outcrops in the East China Sea that it controls but Beijing claims.
Guam and Tinian are about 1,500 miles (2,414 kilometers) south of Tokyo. They're about the same distance to the east from Manila, Philippines.