South Korea said Friday it had successfully test-fired a new ballistic missile capable of carrying a one-tonne payload to any part of North Korea.

The launch was carried out March 23, just two days before North Korea test fired two medium-range ballistic missiles capable of striking Japan.

The announcement of the test is likely to fuel the current tensions on the Korean peninsula which saw the two rivals fire hundreds of live shells into each other's territorial waters earlier this week.

The new South Korean missile, capable of carrying a one-tonne payload up to 500 kilometres (310 miles), was developed under an agreement reached in 2012 with the United States to almost triple the range of the South's ballistic missile systems.

The United States stations 28,500 troops in South Korea and guarantees a nuclear "umbrella" in case of any atomic attack.

In return, Seoul accepts limits on its missile capabilities and had previously operated under a range and payload ceiling of 300 kilometres and 500 kilograms (1,100 pounds).

Given the ambitions of nuclear-armed North Korea's own missile programme, the South had long argued for the limits to be extended.

The 2012 agreement, which was denounced as a provocation by Pyongyang, allows the South to deploy missiles with a maximum range of 800 kilometres.

While the maximum payload for that range remains 500 kilograms, the two parameters are inversely linked, so that for shorter ranges corresponding payload increases are allowed.

Just one month ago, inter-Korean relations appeared to be enjoying something of a thaw.

In February the two rivals had rare, high-level talks, after which they held the first reunion in more than three years for families divided by the 1950-53 Korean War.

Even when annual South Korean-US military exercises began at the end of February, the protests from Pyongyang were relatively muted, and there was talk of further high-level meetings and greater cooperation.

But the mood soon soured, and recent weeks have seen North Korea conduct a series of rocket and missile tests, culminating last month in the test-firing of the two medium-range ballistic missiles.

On Monday, North Korea conducted a live-fire drill along the disputed maritime border. After some shells crossed the boundary, South Korea responded and the two sides fired hundreds of artillery rounds into each other's waters.

North Korean leader Kim Jong-Un warned this week that the situation on the peninsula was "very grave" and vowed to "thoroughly crush" what he called a US-engineered policy of hostility.

N. Korea slams South's missile test 'farce'
Seoul (AFP) April 06, 2014 - North Korea has slammed the South's recent ballistic missile test, calling it a "farce" aimed at showing off Seoul's military strength in the face of threats from Pyongyang.

Seoul said Friday it had successfully test-fired a new ballistic missile capable of carrying a one-tonne payload up to 500 kilometres (310 miles), suggesting it could hit any part of the North.

The launch was carried out on March 23, just three days before the North test-fired two medium-range ballistic missiles capable of striking Japan.

A spokesman for the North's military heaped derision on Seoul's rocket test late Saturday, pointing to its range of "just 500 kilometres."

"Great irony is that (the South is) claiming that they did a great job by conducting a test-fire of a ballistic missile with a range of just 500 kilometres," state-run KCNA quoted the official as saying.

Tensions between the two Koreas were heightened further by rare exchanges of fire across the tense Yellow Sea border on March 31.

The North dropped more than 100 shells across the sea border during a live-fire drill, prompting Seoul to fire back about 300 volleys.

The North's spokesman claimed the South's "poor military reaction" to the drill drew criticism at home, leading it to carry out the missile test to "calm the mounting accusation and derision".

"This farce only brought disgrace to them," said the spokesman.

The isolated and nuclear-armed North is known to have mid-range Rodong-class missiles capable of hitting targets 1,000-1,500 kilometres away.

Pyongyang's test-firing of two Rodong missiles on March 26 -- its first launch of a mid-range missile since 2009 -- followed a series of rocket and short-range missile tests by the North in recent weeks.

The launches were seen as an angry protest at Seoul-Washington joint army drills ongoing in the South, which the North habitually slams as a rehearsal for invasion.

South Korea's new missile was developed under an agreement reached with the US in 2012 to near-treble the range of the South's ballistic missile systems.

In return, Seoul accepts limits on its missile capabilities.

The 2012 agreement -- denounced as a provocation by Pyongyang -- allows Seoul to deploy missiles with a maximum range of 800 kilometres.

The US also stations 28,500 troops in the South and guarantees a nuclear "umbrella" in case of atomic attack.

The United States said Sunday it plans to send two more missile defence warships to Japan to counter the threat posed by North Korea's "provocative" actions.