North Korea defended its latest ballistic missile launch and slammed UN Security Council condemnation in a defiant statement Wednesday, as tensions escalate over the reclusive state's recent behaviour.

The communique from the North's foreign ministry came as investigators in Malaysia probe the shock assassination of Kim Jong-Un's half-brother Monday.

The North's leader has been trying to strengthen his grip on power in the face of growing international pressure over his country's nuclear and missile programmes.

The United Nations Security Council, which includes the North's only major ally China, sharply castigated Pyongyang on Monday for the missile test a day earlier, describing it as a "grave violation" of UN resolutions and threatening "further significant measures".

The rocket launch was the first since US President Donald Trump came to power and was seen as a challenge to the new American leader, who has vowed a strong response to the provocation.

The country is barred under UN resolutions from carrying out ballistic missile launches or nuclear tests.

The North said the Council should "face squarely our advance into securing a strategic position as a nuclear state," according to a statement quoting a spokesman for the foreign ministry, carried by state media KCNA Wednesday.

"We flatly reject the UN Security Council statement that raises issues with a sovereign state's right to self-defense," the statement added.

However, there was no statement from Pyongyang about the death in Kuala Lumpur of Kim Jong-Nam, once tipped as heir apparent.

North Korea has blasted off a series of missiles in the last year and conducted two nuclear tests in its quest to develop a weapons system capable of hitting the US mainland.

The latest rocket -- said by Pyongyang to be able to carry a nuclear warhead -- flew east for about 500 kilometres (310 miles) before falling into the Sea of Japan (East Sea), South Korea's defense ministry said.

The Security Council has imposed six sets of sanctions since Pyongyang first tested an atomic device in 2006.