South Korean troops take part in a combined exercise with U.S. Marines at the Korea Combat Training Center in the mountainous county of Inje, in this undated file photo provided by the Army, March 28. Yonhap

U.S. Marines have joined a large-scale combined exercise at a high-tech training facility in South Korea for the first time, the South's Army said Thursday, amid efforts to boost readiness against North Korean threats.

The two-week exercise began March 19 at the Korea Combat Training Center in the mountainous county of Inje, 126 kilometers northeast of Seoul, involving some 3,600 troops, including a company from the U.S. 3rd Marine Division based in Okinawa, Japan.

The exercise also mobilized soldiers from the Army's 25th Infantry Division, as well as some 230 combat assets, including tanks, armored vehicles and helicopters, with participants staging attack and defense operations for three days each without sleep.

The Army training ground operates an opposition force that participating units battle with and the facility employs a laser engagement system for troops to simulate combat.

"What we looked to get out of this training is to further the relationship between the ROK and U.S. Marine Corps and to increase our ability to partner with the ROK Army in future combat operations," U.S. Marine Corps Capt. Nicholas Bayuk, who took part in the exercise, said in footage released by the South Korean Army.

ROK stands for South Korea's official name, the Republic of Korea.

The U.S. 3rd Marine Division is one of the first reinforcement forces to be deployed to the Korean Peninsula in a contingency, according to the Army.

The two Koreas still technically remain at war as the 1950-53 Korean War ended in an armistice, not a peace treaty. (Yonhap)