It reportedly includes three infantry battalions, a cavalry squadron for reconnaissance, a field artillery battalion, an anti-tank company and a military intelligence company.

US soldiers took note of their South Korean counterparts' skills and partnerships.

"What I have noticed is that the Korean military is very diverse and intelligent," Staff Sgt. Rebecca Osborn, the forward brigade provost marshal officer, was quoted as saying.

"The Korean’s technique for certain fighting roles ... may not be that far off from ours because their forces have been training more frequently with the American military."

He added "their tactics differ from ours and we learn from them just like they learn from us."

A team of US marines also practiced joint parachute operations with South Korean marines as part of Korea Marine Exercise Program last week.

After a simulator-using practice, they actually jumped together out of a UA Army CH-47 Chinook, the PACOM said.

The US Marine Corps' F-35 Lightning II aircraft based in Japan also joined the KMEP, the first time for the stealth fighter to hold a drill in Korea's aerospace.

Around 28,500 American service members are stationed in Korea to help defend against North Korea.

The allies hold massive combined trainings including Key Resolve and Foal Eagle each year, drawing a number of American troops abroad as well.

The command-post Key Resolve drill finished last week after a two-week run, while the Foal Eagle field training will last through the end of next month.

This year's exercises came as the North is apparently preparing for another nuclear test and additional missile launches.

The allies repeatedly emphasized the annual practice is defensive in nature, but Pyongyang views it as a rehearsal for invasion and threatens to retaliate.

In particular, the North's military has reacted sensitively to reports that this year's joint drills have involved elite US Special Forces and strategic weapons for a pre-emptive strike under the new strategy, known as Operations Plan 5015.

Contrary to the old OPLAN 5027, based on retreat, realignment and retaliation plans in case of the North's invasion, it calls for a "preventive strike" in advance on the enemy's key military facilities and top leaders including Kim Jong-un.

The North's military said in a statement Sunday that the allies are seeking to eliminate the North's leadership.

The General Staff Department of the North Korean People's Army said it stands ready to "mercilessly smash the enemy's moves with its own style of special operation and pre-emptive attack."

Meanwhile, the US Forces Korea would no confirm whether the OPLAN 5015 has been applied to this year's drills and the exact number of US commandos mobilized.

"We do not discuss such intelligence-related issues in public," a USFK official said. (Yonhap)