North Korea on Tuesday appeared to have tried and failed with a fresh ballistic missile launch in violation of existing UN resolutions, South Korea's defence ministry said.

The ministry declined to speculate on the missile type, but local media cited military sources as saying it was a powerful, medium-range Musudan missile that has already undergone three failed launches this year.

UN resolutions ban North Korea from any use of ballistic missile technology, although it regularly fires short-range missiles into the sea off its east coast.

Tuesday's failed effort came with tensions still running high on the divided Korean peninsula following the North's fourth nuclear test in January and long-range rocket launch a month later.

The defence ministry in Seoul said the missile test took place at around 5:20 am South Korean time (2020 GMT Monday) near the eastern port city of Wonsan.

"We believe that it was a failure," said Jeon Ha-Gyu, spokesman for the South Korean Joint Chiefs of Staff

"As to why and how it failed, we are in the process of analysing that and can't give more details at the moment," Jeon told a press briefing.


Further provocations

"We are maintaining a strong defence posture with potential further provocations by the North in mind," he added.

In April, the North failed three times to test fire a Musudan, which has an estimated range of anywhere between 2,500 and 4,000 kilometres (1,550 to 2,500 miles).

The lower range covers the whole of South Korea and Japan, while the upper range would include US military bases on Guam.

In Tokyo, public broadcaster NHK said the Japanese government had put its military on pre-emptive alert Monday with orders to intercept any North Korean missile that threatened Japanese territory.

First unveiled as an indigenous missile at a military parade in Pyongyang in October 2010, the Musudan has never been successfully flight-tested.

The three failures in April were seen as an embarrassment for the Pyongyang leadership, coming ahead of a party congress in May that was meant to celebrate the country's achievements.

During the congress, North Korean leader Kim Jong-Un personally extended an offer of military dialogue with the South aimed at easing tensions.

The proposal was repeated several times by the North's military, but Seoul dismissed all the overtures as insincere "posturing" given Kim's vow at the same congress to push ahead with the country's nuclear weapons programme.


Military breakthroughs

Pyongyang had hailed a series of technical military breakthroughs in the months leading up to the May party congress.

They included miniaturising a nuclear warhead to fit on a missile, developing a warhead that can withstand atmospheric re-entry, and building a solid-fuel missile engine.

It also said the North had successfully tested an engine designed for an inter-continental ballistic missile (ICBM) that would "guarantee" an eventual nuclear strike on the US mainland.

Outside experts have treated a number of the claims with scepticism, while acknowledging that the North's nuclear and ballistic missile programmes have both made significant strides.