The weeklong exercises involving the US, UK, France and Japan were intended to show support for the free passage of vessels in international waters amid concerns China may restrict access to the South China Sea.
The French catamaran ran aground just offshore and didn't hit coral or spill any fuel, said Jeff Landis, a spokesman for Naval Base Guam. No one was injured. Today's landing was meant to be a rehearsal for a drill at Tinian island on Saturday, Landis said.
"I have directed that we stop all operations associated with this exercise until we conduct a further assessment of the situation as we gather all the facts," Grimes said.
"NOAA in Honolulu is aware and is collecting information about the incident," said Michael Tosatto, administrator of a National Oceanographic and Atmospheric Administration regional office.
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The drills around Guam and Tinian islands were scheduled to include amphibious landings, delivering forces by helicopter and urban patrols.
China claims virtually the entire South China Sea and has tried to fortify those claims by building islands some with runways, radars and weapons systems on seven mostly submerged reefs.
The reclamation work is opposed by other governments that claim the atolls and by the United States, which insists on freedom of navigation in international waters.
This week members of the Senate Foreign Relations Committee expressed concern that the US hasn't conducted freedom-of-navigation operations since October. Republican Bob Corker, Democrat Ben Cardin and five other senators wrote the letter to President Donald Trump, saying they supported a recent US military assessment that China is militarising the South China Sea and is continuing a "methodical strategy" to control it.
Japan claims a group of rocky, uninhabited outcrops in the East China Sea that Beijing claims. Japan calls the islands Senkaku while China calls them Diaoyu.
Guam and Tinian are about 1,500 miles (2,400 kilometers) south of Tokyo and about the same distance to the east from Manila, Philippines.