Seoul, Aug 19 (IANS): South Korea and the US kicked off a major combined military exercise for its 11-day run Monday to bolster their joint defence readiness amid advancing North Korean military threats.

The annual Ulchi Freedom Shield (UFS) exercise, which runs through August 29, got underway in the face of growing concerns over Pyongyang's continued weapons development, highlighted by its launches of 37 ballistic missiles this year alone and heightened cross-border tensions from the North's recent trash balloon campaign, Yonhap news agency reported.

Based on an all-out war scenario, the UFS features main computer simulation-based command post exercise, concurrent field training and civil defence drills, according to the South's Joint Chiefs of Staff (JCS).

While the exercise will be similar in scale to the previous year, involving around 19,000 South Korean troops, it will include 48 field training events, such as amphibious landing and live-fire drills, up from 38 field events conducted last year. The number of brigade-level exercises will also increase to 17 this year, compared with four from the previous year.

The JCS said the exercise will further strengthen the allies' capability and readiness to respond to any provocations and defend against North Korea's weapons of mass destruction by conducting multi-domain exercises utilising a variety of assets, including land, sea, air, cyber and space.

During the exercise period, the government-led Ulchi civil defence drill will involve a scenario simulating a North Korean nuclear attack for the first time, a source said, while the joint military exercise will not incorporate such a scenario.

North Korea has long denounced the allies' joint exercises as a rehearsal for an invasion against it and has a track record of staging weapons tests in response.

During his visit to a western front-line unit last week, JCS Chairman Adm. Kim Myung-soo ordered troops to retaliate immediately in case of any provocations, saying the North is likely to use the allies' exercise as a pretext to stage provocations.

On Sunday, the Institute for American Studies of the North Korean foreign ministry condemned the Ulchi exercise as the "most offensive and provocative war drills for aggression" in a statement carried by the Korean Central News Agency.

"We will continue to make crucial efforts to build up strong defence capabilities for creditably defending our state sovereignty, security, interests and territorial integrity and change the security environment of the Korean peninsula and the region in our favour," it said.

South Korea and the US have rejected the accusation, describing their drills as defensive in nature.