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.

Kim Jong-Un inspects plans for a missile attack on Guam (
Image:
AFP)
An anti-terror drill in South Korea (
Image:
REUTERS)
Members of South Korean Special Weapons Attack Team (SWAT) (
Image:
Rex Features)

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.

South Korean combat policemen and people take part in an anti-terrorism drill (
Image:
Rex Features)
The South Korean and US military forces joint exercise is held from 21 to 31 August (
Image:
Rex Features)
The South Korean and US military forces joint Ulchi Freedom Guardian (UFG) exercises (
Image:
Rex Features)

"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.