The United States and South Korea began their biggest combined military training in years – heightening their defence posture against the growing North Korean nuclear threat.
It's unclear whether the drills will draw yet another response from Pyongyang, which has pushed its weapons testing activity to a record pace this year while repeatedly threatening conflicts with Seoul and Washington amid a prolonged stalemate in diplomacy.
The Ulchi Freedom Shield exercises, running until 1 September in South Korea, include aircraft, warships, tanks and potentially tens of thousands of troops.
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While Washington and Seoul describe their exercises as defensive, North Korea portrays them as invasion rehearsals that justify its nuclear weapons and missile development.
Cho Joong-hoon, a spokesperson of South Korea's Unification Ministry, which handles inter-Korean affairs, said the South has not immediately detected any unusual activities or signs from the North.
The US and South Korea had cancelled some of their regular drills and reduced others to computer simulations in recent years to create space for diplomacy with North Korea and because of COVID-19 concerns.
Ulchi Freedom Shield, which started along with a four-day South Korean civil defence training programme led by government employees, will reportedly include simulated joint attacks, frontline reinforcements of arms and fuel and removals of weapons of mass destruction.
The drills came after North Korea last week dismissed South Korean President Yoon Suk Yeol's offer to exchange denuclearisation steps and economic benefits, accusing Seoul of recycling proposals Pyongyang has long rejected.
Watch: North Korea launches first intercontinental ballistic missile in more than four years.
Kim Yo Jong, the increasingly powerful sister of North Korean leader Kim Jong Un, described Mr Yoon's proposal as foolish and stressed the North has no intentions to barter away an arsenal her brother apparently sees as his strongest guarantee of survival.
She harshly criticised Mr Yoon for continuing military exercises with the US and also for Seoul's failure to stop South Korean civilian activists from flying anti-Pyongyang propaganda leaflets and other "dirty waste" across the border by balloon.
She also ridiculed US-South Korean capabilities for monitoring the North's missile activity, insisting Seoul wrongly identified the launch location of the North's latest missile tests last Wednesday, hours before Mr Yoon at a news conference urged Pyongyang to return to diplomacy.
Ms Kim earlier this month warned of "deadly" retaliation against South Korea over a recent North Korean COVID outbreak, which Pyongyang dubiously claims was caused by leaflets and other objects floated by southern activists.
There are concerns the North may try to raise tensions sometime around the allied drills.