One of Asia's largest war games kicks off in Thailand on Tuesday with scaled back U.S. involvement, highlighting tensions between the longtime allies over Thailand's lack of democracy at a time of growing Chinese influence in Southeast Asia.

Some 8,500 soldiers from seven nations — Thailand, the U.S., Japan, South Korea, Indonesia, Singapore and Malaysia — will take part in Cobra Gold's core activities over the 11 days of exercises, according to a Thai military statement. A further 21 nations will participate in reduced roles, including China as part of a humanitarian assistance session.

Though the U.S. sees Cobra Gold as "an integral part of the U.S. commitment to strengthen engagement in the region," for a second straight year it is turning up with a reduced contingent, said Melissa Sweeney, a spokeswoman at the U.S. Embassy in Bangkok. "The 2016 exercise will remain reduced in size to limit the type of activities it contains to reflect our concerns with Thailand's political developments," she said.