The U.S. and South Korea kicked off their annual joint military exercises Sunday.
Seoul's defense ministry said the springtime Foal Eagle kicked off with 11,500 US troops and 300,000 South Korean soldiers taking part in the field training exercise, one of the largest military drills conducted annually in the world, SBS reported.
A two-week, computer-simulated exercise known as Key Resolve is due to start on April 23 with some 12,200 Americans and 10,000 South Korean military personnel.
Military officials in Seoul have said the scale of the exercises would not go beyond those seen in previous years.
About 28,500 US service members are based in South Korea, which technically remains at war with the North after their 1950-53 conflict ended in an armistice instead of a peace treaty.
Ssangyong is expected to last until next Sunday, while the entire Foal Eagle drill will run for four weeks, down from last year's eight-week program, which kicked off on March 1.
A Pentagon spokesman said the drills will feature about 23,700 US troops and 300,000 South Korean forces.
The allies are holding the drills later than usual this year after postponing them to help pave the way for the North's participation in the Olympics and Paralympics, which were held in the alpine town of Pyeongchang.
The drill - which was delayed to avoid clashing with February's Winter Olympics in the South - will be held for a month in April, about have the time it usually lasts. Moreover, US supercarriers or nuclear submarines were not deployed to the military exercise. But its leader Kim Jong Un reportedly softened his tone when he met South Korean envoys in March. In a meeting last week with Chinese President Xi Jinping in Beijing, Kim expressed his willingness to discuss North Korea's potential de-nuclearization.