North Korea has notified of a planned satellite launch in June.
North Korea will launch its first military reconnaissance satellite in June for live monitoring of US military activities, state media KCNA reported.
In a statement carried by the KCNA news agency, Ri Pyong Chol, vice-chairman of the Central Military Commission of the ruling Workers' Party, denounced joint military exercises by the United States and South Korea as openly showing their "reckless ambition for aggression."
South Korean and US forces began live-fire exercises simulating a "full-scale attack" from North Korea last week in what they said were the biggest such drills to demonstrate their "overwhelming" military capability against the North's threats.
North Korea's Ri said the drills required Pyongyang to have the "means capable of gathering information about the military acts of the enemy in real time."
The statement did not specify the exact launch date, but North Korea has notified Japan of the planned launch between May 31 and June 11, prompting Tokyo to put its ballistic missile defences on alert.
Nuclear-armed North Korea says it has completed its first military spy satellite and leader Kim Jong Un has approved final preparations for the launch.
Japan vowed to shoot down any projectile that threatens its territory, saying any North Korean missile launch would be a serious violation of UN Security Council resolutions.
Tokyo expects North Korea to fire the rocket carrying its satellite over Japan's southwest island chain as it did in 2016, a defence ministry spokesperson said.
Analysts say the new satellite is part of a surveillance technology program that includes drones, aimed at improving the ability to strike targets in wartime.
"We will take destructive measures against ballistic and other missiles that are confirmed to land in our territory," Japan's defence ministry said in a statement.
Japan would use its Standard Missile-3 (SM-3) or Patriot Missile PAC-3 to destroy a North Korean missile, it added.
Japanese Prime Minister Fumio Kishida told reporters: "We strongly urge North Korea to refrain from launching," his office said on Twitter, adding it would co-operate with the US, South Korea and other countries and do all it could to collect and analyse information from any launch.
A US State Department spokesperson said any North Korean launch that uses ballistic missile technology, including that which is used to put a satellite in orbit, would violate multiple UN resolutions.
The US urges North Korea "to refrain from further unlawful activity and calls on Pyongyang to engage in serious and sustained diplomacy," the spokesperson said.
South Korea joined in calling on the reclusive North to scrap its plan, which it described as "illegal."
"If North Korea presses ahead, it will pay the price and suffer," a spokesperson from the South's foreign ministry said in a statement.