Rahm Emanuel, Washington's outspoken ambassador to Japan, wrote in a post on X: "1st: Defense Minister Li Shangfu hasn't been seen or heard from in 3 weeks.
China's defence ministry did not immediately respond to requests for comment.
On the trip, Wat met with China's navy commander, Dong Jun and other navy leaders, Singapore's defence ministry said on its website.
Singapore's defence ministry did not immediately respond to a request for comment.
Military observers and diplomats are closely watching whether China will go ahead with plans to hold the Beijing Xiangshan Forum - an annual international security summit normally hosted by China's defence minister - in late October.
Persons:
Li Shangfu, Li, Rahm Emanuel, Washington's, Li Shangfu hasn't, Mao Ning, Qin Gang, Qin, Emanuel, Barack Obama, Matthew Miller, Sean Wat, Wat, Dong Jun, Lloyd Austin, Yew Lun Tian, Laurie Chen, Martin Pollard, Yukiko Toyoda, Xinghui, John Geddie, Neil Fullick, Lincoln, Gerry Doyle
Organizations:
Defence, Financial Times, U.S, Street Journal, Defense, Navy, Liberation, Rocket Force, . State Department, Reuters, Military, Beijing Xiangshan, U.S . Defence, Australian National University, Thomson
Locations:
BEIJING, TOKYO, U.S, Beijing, Japan, Vietnam, Tokyo, States, China, Singapore, United States, Xinghui Kok