The North's military also said Sunday it will no longer be bound to the armistice agreement that ended the 1950-53 Korean War.
The threats come amid diplomatic efforts to revive stalled negotiations on ending North Korea's nuclear weapons program. North Korea quit the disarmament talks and conducted its second atomic test last year, drawing tighter U.N. sanctions.
North Korea wants the sanctions lifted and peace talks with the U.S. on formally ending the Korean War, which ended in a truce, not a peace treaty. The U.S., South Korea and Japan are urging the North to first return to the nuclear talks and make progress on denuclearization.
The North Korean military on Sunday condemned the U.S.-South Korean drills as preparation for an invasion. It said the process of denuclearization of the Korean peninsula will come to a standstill and the North will bolster its nuclear deterrent.
"The revolutionary armed forces of (North Korea) will be left with no option but to exercise merciless physical force as the rival is set to do harm to the (North)," the military's mission at the truce village of Panmunjom said in a statement carried by the country's official Korean Central News Agency.
North Korea has escalated its threats against South Korea and the U.S. over the planned drills. Last week, the North vowed to strengthen its nuclear deterrent and its means of delivery -- an apparent reference to missiles. Last month, the North also threatened a "powerful" -- even nuclear -- attack if the drills go ahead.
The U.S., which keeps about 28,500 troops in South Korea, plans to conduct the military exercises on Monday as planned. The U.S. and South Korea say the maneuvers are purely defensive.
Koh Yu-hwan, a professor at Seoul's Dongguk University, dismissed North Korea's statement as rhetoric.
"The North's strong protest is not unusual as it also protested during previous drills," Koh said.￼
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