The US and Japan have launched a major field training exercise in Japan's southern Miyazaki Prefecture. It comes amid what is possibly both sides' biggest joint military maneuvers, which began on Friday.

The US military downplayed the drills, saying the exercise involves just 550 Japanese Self-Defense Force infantry members and 215 US marines and sailors. But local media reports suggest that more than 34-thousand Japanese and 10-thousand American troops are participating in the drills.

A South Korean military contingent is observing the maneuvers, which conclude next Wednesday.