"The U.S. should take the whole responsibility for catastrophic results from its reckless war game as it choose to make a military confrontation with us", its spokesman said in a statement.
US Joint Chiefs of Staff chairman Gen. Joseph Dunford told reporters during a visit to Beijing there would no scaling back of planned military exercises despite the recent tensions with North Korea.
North Korea routinely issued warnings before and during the allies' drills, but this year it came amid heightened tensions between Washington and Pyongyang following exchanges of bellicose rhetoric.
Tensions are high on the Korean Peninsula, especially since North Korea recently test-launched two intercontinental ballistic missiles (ICBM) that experts say could reach US territory.More news: Dems risk culture war fight in Charlottesville response
The exercise involves 17,500 American troops and 50,000 South Korean soldiers, according to the U.S. military command in South Korea and Seoul's defence ministry.
A report Pyongyang has earned millions of dollars in exports seemed likely, meanwhile, to raise doubts about the impact of sanctions to pressure North Korea into dismantling its nuclear and ballistic missile programmes.
South Korean President Mun Gehin said the exercises are entirely defensive and not meant to provoke tension in the region. However, the US and South Korea maintain they are purely defensive.
South Koreans opposed to the joint U.S.
"No one can guarantee that this will not escalate into a real war", it said, calling the annual drills a "rehearsal for nuclear war" and the "most naked expression of hostility" toward the North.More news: US, South Korean Troops Drill Amid Standoff with North
North Korea's rapid progress in developing nuclear weapons and missiles capable of reaching the United States mainland has fueled a surge in regional tension and UN-led sanctions appear to have failed to bite deeply enough to change its behaviour.
"We think that South Korea and the United States holding joint drills is not beneficial to easing current tensions or efforts by all sides to promote talks", she told a daily news briefing.
Officials said there will be no field training, such as live-fire exercises or tank maneuvers.
USA and South Korean troops kicked off their annual drills Monday that come after President Donald Trump and North Korea exchanged warlike rhetoric in the wake of the North's two intercontinental ballistic missile tests last month. During last year's Ulchi drills, North Korea test-fired a submarine-launched ballistic missile that flew about 310 miles in the longest flight by that type of weapon.
Only weeks ago it said it was considering firing a salvo of missiles towards the US Pacific territory of Guam. About 17,500 USA service members are participating in the exercise this month, down from 25,000 previous year, according to the Pentagon.More news: First round of NAFTA talks conclude between US, Canada and Mexico
And, the tensions were ratcheted up further when President Donald Trump made threats of fire and fury to North Korea.
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