A North Korean missile appeared to have exploded on Wednesday just after it was launched, the U.S. and South Korean militaries said after detecting the latest in a series of weapons tests by the nuclear-armed state that have alarmed the region.

The launch attempt was made from near the city of Wonsan, on North Korea's east coast, the same place from where it launched several intermediate-range missiles last year, all but one of which failed.

"U.S. Pacific Command detected what we assess was a failed North Korean missile launch attempt ... in the vicinity of Kalma," Commander Dave Benham, a spokesman for U.S. Pacific Command, said in a statement, referring to an air field in Wonsan.

"A missile appears to have exploded within seconds of launch," Benham said, adding that work was being carried out on a more detailed assessment.

A South Korean military official told Reuters the missile appeared to have exploded just after it was launched.

"It may have exploded right after it took off from a launch pad," said military official, who declined to be identified.

It was not clear what type of missile it was. The South Korean defense ministry said it was conducting analysis to determine further details.

The increasing frequency of the missile tests has fueled a growing sense of urgency over how to respond to the isolated, unpredictable state.

North Korea to pursue "acceleration" of nuclear, missile programmes

North Korea has nothing to fear from any US move to broaden sanctions aimed at cutting it off from the global financial system and will pursue "acceleration" of its nuclear and missile programs, a North Korean envoy told Reuters on Tuesday.

This includes developing a "pre-emptive first strike capability" and an inter-continental ballistic missile (ICBM), said Choe Myong Nam, deputy ambassador at the North Korean mission to the United Nations in Geneva.

"We strengthen our national defence capability as well as pre-emptive strike capabilities with nuclear forces as a centrepiece," Choe said.

North Korea asked to refrain from "provocative actions"

Asked to comment on Choe's remarks, a US State Department spokeswoman, Anna Richey-Allen, called on North Korea "to refrain from provocative actions and inflammatory rhetoric... and to make the strategic choice to fulfil its international obligations and commitments and return to serious talks.”

Choe declined to give technical details of North Korea's latest rocket engine test on Sunday ─ seen as a possible prelude to a partial ICBM flight ─ calling it a great historical event that would lead to "fruitful outcomes".

"I can tell you for sure that the inter-continental ballistic rockets of the DPRK will be launched at any time and at any place as decided by our Supreme Leadership," Choe said, recalling leader Kim Jong Un's pledge in a New Year's address.

Analysts say North Korea has likely mastered the technology to power the different stages of an ICBM and may show it off soon, but is likely still a long way from being able to hit the mainland United States.

"The United States has been talking about launching preemptive strikes at North Korea," Choe said. "And we have been prepared to deter, to counter-attack such attacks on the part of the United States.

"We would utilise every possible means in our hands and the inter-continental ballistic rocket is one of them."

North Korea has been under sanctions for "half a century" but the communist state survives by placing an emphasis on juche or "self-sufficiency", he said.

His country wants a forum set up to examine the "legality and legitimacy of the sanctions regime".

He denounced joint annual military exercises currently being carried out by the United States and South Korea on the divided peninsula and criticised remarks by Tillerson during his talks with regional allies last week.

"All he was talking about is for the United States to take military actions on DPRK," Choe said, using the acronym for the Democratic People's Republic of Korea.

North Korea rejects claims by Washington and Seoul that the military drills are defensive. They involve strategic nuclear bombers and a nuclear submarine, Columbus, that recently entered South Korean ports, he said.

"In the light of such huge military forces involved in the joint military exercises, we have no other choice but to continue with our full acceleration of the nuclear programs and missile programs. It is because of these hostile activities on the part of the United States and South Korea." -Reuters