North Korea has angrily claimed the US and South Korea are "preparing for invasion" after they began joint military drills.
State television in Kim Jong-Un's regime accused the allies of getting ready to carry out a pre-emptive attack.
Tensions remain high after President Donald Trump threatened the country with "fire and fury" if it failed to heed warnings about its nuclear programme.
The North threatened missiles strikes on US territory in Guam in retaliation.
Kim Jong-Un said those plans were being postponed last week, but there was fresh outrage on Monday.
North Korea said it was watching "every move" of the military exercises being carried out by the South and the US.
South Korean President Moon Jae-in said the joint drills, called Ulchi Freedom Guardian, were purely defensive and did not aim to increase tension on the peninsula.
"There is no intent at all to heighten military tension on the Korean peninsula as these drills are held annually and are of a defensive nature," Moon told cabinet ministers.
"North Korea should not exaggerate our efforts to keep peace nor should they engage in provocations that would worsen the situation, using (the exercise) as an excuse," he said.
The joint U.S.-South Korean drills last until August 31 and involve tens of thousands of troops as well as computer simulations designed to prepare for war with a nuclear-capable North Korea.
The United States also describes them as "defensive in nature", a term North Korean state media has dismissed as a "deceptive mask".
"It's to prepare if something big were to occur and we needed to protect ROK," said Michelle Thomas, a U.S. military spokeswoman, referring to South Korea by its official name, the Republic of Korea.