South Korea and the United States Monday began a major military exercise, a Seoul spokesman said, despite North Korea's threats of possible retaliation.A spokesman for the Joint Chiefs of Staff said the annual Key Resolve drill had started but gave no details. The computerised command post exercise will continue until March 9.
The North's National Defence Commission has denounced the annual drill -- which will be followed by joint air, ground and naval field training exercise Foal Eagle from March 1 to April 30 -- as a "silent declaration of war".
"Our army and people will foil the moves of the group of traitors to the nation and warmongers at home and abroad for a new war with a sacred war of our own style," the commission, the North's top ruling body, said on Saturday.
The United States bases 28,500 troops in the South. The North habitually denounces its annual exercises with South Korean forces as a rehearsal for invasion.
Seoul and Washington say the drills are defensive in nature.
The North has taken a hostile tone with the South since its leader Kim Jong-Il died on December 17 and was replaced by his youngest son Jong-Un.
The new leader has been appointed armed forces chief and has visited several units in an apparent attempt to burnish his military credentials.
Kim inspected two army battalions at a base near the border with the South, state media said Sunday, adding that one of them had staged the deadly shelling of a South Korean island in November 2010.
The leader ordered "a powerful retaliatory strike" if Monday's drills intrude on North Korean territory, it said.
Pyongyang's state news agency Monday described Key Resolve as "an unpardonable infringement upon the sovereignty and dignity" of the North while it is still in mourning for the late leader.
The South's military has strengthened monitoring of the North's activities to guard against potential attacks, Yonhap news agency said Sunday.
It said RF-4 and U-2 reconnaissance aircraft would be fully mobilised and F-15K fighter jets would be on emergency standby.
Artillery units deployed near the land border will also stand ready to immediately hit back if attacked, it said. The defence ministry declined to comment.
Cross-border tension has been high since Seoul accused Pyongyang of torpedoing a warship with the loss of 46 lives near the tense sea border off the west coast in March 2010.
The North denied involvement but went on to shell Yeonpyeong island later that year, killing four people and sparking brief fears of war.
Hong Hyun-Ik of the South's Sejong Institute think-tank said Kim Jong-Un's latest visit was aimed at forging an image as a brave young leader and to garner loyalty from the powerful military.
"It's eventually aimed to further cement his leadership by highlighting the country's Songun (military-first) policy and solidify the new leadership as quickly as possible," Yonhap quoted Hong as saying.