North Korea threatened retaliation on Thursday after the United States flew long-range B-1B bombers over South Korea during a joint training exercise.

The drill took place on Tuesday, which North Korea considers as an invasion rehearsal for an attack against it. It is particularly cautious about the American use of long-range bombers, aircraft carriers and nuclear-powered submarines.

According to South Korea's Defense Ministry, the joint training, a routine practice between both countries, showed their combined military capabilities against North Korea's advancing nuclear program.

The joint air drill happened on the 113th anniversary of the birthday of Kim Il Sung, the founder of North Korea, which raised tensions.

What did North Korea say?

The strategic deployment of US long-range bombers in the region has become a "reckless bluffing," said North Korea's Defense Ministry in a statement carried by state news agency KCNA.

"The recent military move of the US and the Republic of Korea [South Korea] is an open threat to the security of our state and a grave provocation that raises the military tension in the region to an extremely dangerous level," KCNA added.

North Korea's Defense Ministry threatened the US to retaliate against its "aggressive attempt to permanently fix the malignant instability element in the security environment of the region," KCNA added.

North Korea often test-launches missiles in response to the US long-range bomber B-1B, which the US Air Force often uses for powerful airstrikes.

South Korea, US announce a large-scale air drills

Jeon Ha-kyu, a spokesperson South Korea's Defense Ministry, said in a briefing that the joint military venture was defensive.

South Korea's Air Force announced on Thursday a large-scale aerial drill called "Freedom Flag" with the US Air Force that will occur twice a year.

The two-week exercise would involve 90 fighter jets and other aerial military assets from South Korea and the US.

Tensions on the Korean Peninsula have escalated in recent years as North Korea continues with weapons tests to modernize its nuclear arsenal and backs Russia's war in Ukraine by providing weapons and troops.

Edited by: Zac Crellin