North Korea said any move to shoot down one of its test missiles would be considered a declaration of war and blamed a joint military exercise between the US and South Korea for growing tensions, state media KCNA said today.

Kim Yo Jong, the powerful sister of leader Kim Jong Un, warned in a statement that Pyongyang would see it as a "declaration of war" if the US took military action against the North's strategic weapon tests.

She also hinted that the North could fire more missiles into the Pacific Ocean.

The US and its allies have never shot down North Korean ballistic missiles, which are banned by the United Nations Security Council, but the question drew new scrutiny since the North suggested it will fire more missiles over Japan.

"The Pacific Ocean does not belong to the dominium of the US or Japan," Kim said.

Analysts have said that if North Korea follows through on its threat to turn the Pacific Ocean into a "firing range", it would allow the isolated and nuclear-armed state to make technical advances in addition to signalling its military resolve.

In a separate statement, the chief of the Foreign News Section at North Korea's Foreign Ministry accused the US of "aggravating" the situation by conducting a joint air drill with a B-52 bomber on Monday and planning US-South Korea field exercises.

The US deployed the B-52 bomber for a joint drill with South Korean fighter jets, in what South Korea's defence ministry said was a show of force against North Korea's nuclear and missile threats.

The two countries will conduct more than 10 days of large-scale military exercises known as the "Freedom Shield" drills starting next week.

Around 28,500 US troops are stationed in South Korea as a legacy of the 1950-1953 Korean War, which ended in an armistice, rather than a peace treaty, leaving the countries technically at war.

- Reuters