The world's eighth declared nuclear power is a secretive and volative regime which for five decades has been technically at war with South Korea and the United States.

It is believed to have produced enough weapons-grade plutonium to make several crude nuclear bombs, according to US and South Korean experts.

The North, which pledges no first use of any nuclear weapons, also has an advanced missile programme although it is not known whether it could arm one with a nuclear warhead.

On July 5, it test-fired seven missiles which fell into the sea - including a Taepodong-2 believed to be technically capable of hitting the United States.

In its October 3 statement, the North pledged never to use nuclear weapons first and strictly to ban the transfer of nuclear weapons and technology.

"The ... nuclear weapons will serve as reliable war deterrent for protecting the supreme interests of the state and the security of the Korean nation from the US threat of aggression and averting a new war..." it said at the time.

North Korea had kept the world guessing for almost 20 years about its progress towards a bomb, declaring only in February 2005 that it possessed nuclear weapons.

The United States had said it would press for mandatory UN sanctions after any test, but played down the prospect of a military response -- something Seoul has also ruled out.

Analysts had said a test may trigger a regional nuclear arms race, and Leave international non-proliferation efforts in tatters.