SEOUL South Korea has proposed bilateral nuclear talks with the isolated North, as Seoul seeks to gauge Pyongyang's sincerity about giving up its nuclear weapons programme in line with past international agreements.
The North has yet to respond to Seoul's request.
Pyongyang has said it wants to restart aid-for-disarmament talks, despite walking out of the forum in 2009 and declaring the six-party format dead.
Seoul says it will sound out if the North Koreans are genuine about denuclearisation and will report back to the other six-party members: the United States, China, Japan and Russia.
Here is look at the North's nuclear arms programme.
HOW ADVANCED IS THE NORTH'S PLUTONIUM PROGRAMME?
The North Korean nuclear weapons programme dates back to the 1980s when it began construction of its Yongbyon complex, about 100 km (60 miles) north of Pyongyang. It consists of a five-megawatt reactor, a fuel fabrication facility and a plutonium reprocessing plant, where weapons-grade material is extracted from spent fuel rods.
The North tested nuclear devices in 2006 and 2009, but still has not shown it has a working nuclear bomb. Proliferation experts say it has enough fissile material for up to 10 nuclear weapons.
Under the terms of a previous aid-for-disarmament agreement, North Korea dismantled the main reactor, and despite restoring parts of the plant, it is still not operational.
WHERE IS THE URANIUM ENRICHMENT PROGRAMME AT?
Last November, North Korea unveiled its uranium enrichment programme, which would give it another path to make atomic weapons, to the outside world. Uranium enrichment can be conducted away from the prying eyes of satellites, and the North can fuel it with its ample supplies of natural uranium.
Although, it was widely known that North Korea had such a programme, foreign experts who saw the facility said they were stunned by its sophistication.
The foreign experts said they were not able to establish whether the plant was designed to produce only low-enriched uranium needed to make fuel for a power plant or the highly enriched uranium for bombs. It is easier to design a nuclear bomb with highly enriched uranium (HEU) than plutonium, but harder to make a nuclear warhead with HEU to mount on a missile.
BUT CAN THE NORTH DELIVER A NUCLEAR BOMB?
Experts say they do not believe the North can miniaturise an atomic weapon to place on a missile, but it is trying to develop such a warhead. It needs more nuclear testing to build one.
North Korea's ageing fleet of Soviet-era bombers would also have difficulty evading the advanced air forces of regional powers to deliver a nuclear bomb outside the country.
But, Washington says the North's long-range ballistic missile programme is moving ahead fast, and that the American mainland could itself come under threat within five years.
The nuclear threat, however, could be delivered by other unconventional means such as aboard a civilian aircraft, boat or van to the target.
Experts agree, however, no nation would dare use a nuclear device against a nuclear-armed state, because the certainty of retribution would far outweigh whatever benefit might be gained. Non-nuclear armed states such as South Korea and Japan fall under Washington's nuclear umbrella.
HOW DOES THE NORTH JUSTIFY ITS NUCLEAR ARMS PROGRAMME?
The North says the world has got it all wrong about its hostile intentions, and that it is only pursuing uranium enrichment for peaceful energy purposes.
As for its plutonium programme, Pyongyang says it was cornered into pursuing nuclear weapons because of the United States' nuclear threat. It says it is as entitled to a deterrent as the Americans, and that when Washington denuclearises it will do the same.
COULD IT SELL THE NUCLEAR TECHNOLOGY?
Apart from the direct threat of a nuclear weapon, the next biggest concern is the proliferation risk Pyongyang poses. Much of the North's income in the past has been generated through arms sales.
Last year, a U.N. report suggested the North may have supplied Syria, Iran and Myanmar with banned nuclear technology. Equally, experts worry about the potential for subsequent proliferation to terrorists.
(Editing by Miral Fahmy)