North Korea said Tuesday it possessed rockets capable of striking the US mainland, as it slammed a new US-South Korean deal to extend the range of the South's missile systems as a provocation for war.

The threat, which analysts largely dismissed as bluster, came after South Korea announced Sunday an agreement with the United States to almost triple the range of its missiles to 800 kilometers (500 miles) to cover the whole of North Korea.

A spokesman for the North's National Defense Commission said the deal was "another conspiracy of the master and the stooge to push the situation on the Korean Peninsula to the extreme... and ignite a war."

In a statement carried by the official Korean Central News Agency (KCNA), he said the North's military, including "strategic rocket forces", had a "scope of strike" that not only covered US and South Korean bases in South Korea, "but also Japan, Guam and the US mainland".

South Korean analysts said the claim was likely to be empty rhetoric, suggesting it was aimed more at boosting military morale under new leader Kim Jong-Un.

"There is no evidence that North Korea has succeeded in tests of a missile with a range long enough to hit the US mainland," said Yun Duk-Min, a professor at Korea National Diplomatic Academy.

North Korea is known to have an inter-continental ballistic missile (ICBM) in development -- the Taepodong-2 -- but it has never been tested successfully.

In April, North Korea failed with a much-hyped rocket launch that Pyongyang said was aimed at placing a satellite in orbit.

The United States and United Nations insisted it was a disguised ballistic missile test using a three-stage variant of the Taepodong-2.

Days after the failed launch, North Korea raised eyebrows by displaying what appeared to be a new set of ICBMs at a military parade to mark the 100th birthday of the North's late founder Kim Il-Sung.

But Western military analysts and UN sanctions experts concluded that the display models were simply mock-ups.

The new agreement announced Sunday with the United States allows the South to deploy missiles with a range of 800 kilometres (500 miles), up from the current limit of 300 kilometres.

The extension not only brings the whole of North Korea within reach of Seoul's rockets, but also parts of China and Japan.

The US 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.

Given the ambitions of nuclear-armed North Korea's own missile programme, the South had long argued for the limits to be extended and negotiations had taken on a new urgency after the North's failed rocket launch in April.

Seoul believes Pyongyang has 1,000 missiles of various types, many of them targeted at the capital or other locations in the South.

Condemning the new US-South Korea deal, the National Defense Commission spokesman said Pyongyang would retaliate "in kind" to any US or South Korean nuclear or missile attack.

He also stressed the desire of the North Korean army and people to "feel the real taste of a war".

Kim Yong-Hyun, a professor at Dongguk University, played down the implied threat.

"North Korea is again talking tough but this is a typical reaction," Kim told AFP.

"It does not necessarily mean it will now double its efforts to develop long-range missiles."