SEOUL, March 13 (Xinhua) -- Combined forces of South Korea and the United States on Monday kicked off the annual command post exercise, codenamed Key Resolve, which is scheduled to last for 11 days.

The computer-simulated exercise between the two allies will continue through March 24, local media reported, citing unnamed military officials.

It followed the launch on March 1 of the joint field training drill with the codename of Foal Eagle that will last by the end of next month.

The Key Resolve is the U.S.-South Korea exercise to reinforce U.S. armed forces to the Korean Peninsula in times of military conflict and repel possible attack from the Democratic People's Republic of Korea (DPRK).

The DPRK has denounced the joint springtime war games as a dress rehearsal for northward invasion.

Peace activists of about 10 local civic groups held a rally, titled The Day of Peace Action, in downtown Seoul on Saturday to protest against the ongoing U.S.-South Korea military exercises and the deployment of Terminal High Altitude Area Defense (THAAD) in South Korean soil.

Two mobile launchers and part of the THAAD system arrived in South Korea a week earlier and was transported to an unknown base of the U.S. Forces Korea (USFK). THAAD is composed of six mobile launchers, 48 interceptors, an X-band radar and a fire and control unit.

This year's Key Resolve drill will reportedly conduct the first computer simulation of operating the THAAD battery, which local media outlets estimated would be deployed in southeast South Korea as early as next month.

South Korea and the U.S. claim that THAAD is defensive in nature as it is aimed to protect from the DPRK missiles targeting the southern port city of Busan, through which the U.S. reinforcement would enter South Korea in times of emergency.

THAAD is aggressive as it boosts arms race and breaks regional strategic balance. The AN/TPY-2 radar installed in South Korea would help the United States and Japan defend from missile attacks, enabling the three allies to peer deep into the territories of China and Russia.

More missile shields will bring more nuclear missiles that can break through the missile defense systems. The loss of the mutual assured destruction (MAD) may trigger a nuclear proliferation in the region.

China and Russia have strongly opposed the THAAD installation since Seoul and Washington abruptly announced the deployment decision in July last year.

The U.S.-South Korea commands will exercise a so-called Operation Plan 5015 during the 11-day Key Resolve drill, according to local media reports. The operation plan includes pre-emptive strikes against the DPRK's nuclear and missile facilities when signs of attack are detected.

This year's Key Resolve command post exercise will be led by South Korea's Joint Chiefs of Staff (JCS) for the first time since 2013. South Korea has yet to restore the wartime operation control of its troops from the U.S., a legacy from the 1950-53 Korean War.

JCS Chairman Lee Sun-jin and USFK commander Vincent Brooks visited USS Carl Vinson, which has participated in the Foal Eagle field training exercise, earlier in the day, according to local media reports. The nuclear-powered U.S. aircraft carrier is scheduled to pay a visit to the Busan port on Wednesday.

The Nimitz-class aircraft carrier and its attendant fleet are accompanied by 24 F/A-18 fighter jets, 10 aerial tankers, 10 S-3A anti-submarine airplanes, six SH-3H anti-submarine helicopters, four EA-6B electronic warfare aircrafts and 4 E-2 airborne early warning aircrafts.

Other U.S. strategic assets to be brought to the drill would be F-35B stealth fighter jets that were deployed in the U.S. military base in Japan in January.