For the first time a South Korean general is commanding annual joint drills with American forces, the U.S. military said on Wednesday, a step toward Seoul's long-delayed goal of gaining command of allied forces in the event of a war.

The allies began on Monday their largest joint military drills in years, known as Ulchi Freedom Shield, with a resumption of field training, aiming to strengthen readiness for potential weapons tests by North Korea.

The exercises include an 11-day "computer simulated, defensc-oriented training event" to improve allied readiness, U.S. Forces Korea (USFK) said in a statement.

In the exercise, U.S. Army Gen. Paul LaCamera, who commands USFK troops, the U.S.-South Korea Combined Forces Command (CFC), and the United Nations Command (UNC), switched positions with his deputy, South Korean Gen. Ahn Byung-seok, USFK said.

The move was based on future command plans outlined by U.S and South Korean defence secretaries last year, LaCamera said in the statement.

"This is significant because, for the first time ever, the CFC deputy commander will take the lead as the future CFC commander," he added.

Since the 1950-1953 Korean War, the American military has retained authority to control hundreds of thousands of South Korean forces alongside the roughly 28,500 U.S. troops stationed in the country if another war breaks out.

President Yoon Suk-yeol has said South Korea is not ready to take operational control of those joint forces, after a push by his predecessor, Moon Jae-in, faced delays over the COVID-19 pandemic and other issues.

Yoon has cited a need for greater surveillance and reconnaissance capabilities, among other factors.

South Korean Defence Minister Lee Jong-sup participated in Wednesday's drills, which the ministry said aimed at better deterring and responding to North Korea's nuclear and weapons of mass destruction (WMD) threats.

North Korea has criticised the joint drills as a rehearsal for invasion, calling them a "hostile policy" that proves Washington and Seoul are truly not interested in diplomacy.