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By Jon Herskovitz

SEOUL, April 30 (Reuters) - North Korea rattled the region in the past week by threatening to conduct a nuclear test and saying it had resumed producing arms-grade plutonium.

The following are some questions and answers about the secretive state's nuclear arms programme:

WHAT IS NORTH KOREA'S NUCLEAR WEAPONS CAPABILITY?

North Korea is thought to have produced enough plutonium for about six to eight weapons and has already produced one rudimentary nuclear device. It likely cannot miniaturise a nuclear weapon to mount on a missile and would need a significant amount of testing to master the technology, weapons experts say. And its Soviet-era bombers would not be able to evade the advanced air forces of the United States, Japan and South Korea to deliver a bomb, which means it may be many years before North Korea can actually threaten the world with a nuclear weapon.

HOW LONG WOULD IT TAKE THE NORTH TO CONDUCT A NUCLEAR TEST?

Impoverished North Korea, whose only nuclear test in October 2006 led to U.N. sanctions, could be ready to test another nuclear device in a matter of weeks, experts said. Politically, North Korea wants to play out its test preparations, many of which can be seen by U.S. spy satellites, as long as possible to increase its leverage in negotiations. Experts believe a second test would not come for several months, if at all.

Experts said the North's only nuclear test was only a partial success because the strength of the blast was relatively low, indicating problems with the weapons design or the fissile material at its core.

WOULD THERE BE MORE THAN ONE?

North Korea probably would only conduct one because it does not want to deplete its meagre plutonium stockpile.

Future testing would depend on its ability to restore its ageing Yongbyon nuclear plant, which was being disabled under a six country disarmament-for-aid deal. The plant can produce about one bomb's worth of fissile material a year.

The United States and others have charged North Korea with having a secret programme to enrich uranium, giving it another avenue to produce nuclear weapons, but experts doubt that the North has seriously developed the programme.

HOW BIG IS THE SECURITY THREAT?

The North's nuclear arms programme is not a major security threat at present because it has not yet shown it can build an effective bomb, nor does it have an effective delivery system.

The biggest security threats posed by the North come from its hundreds of mid-range missiles that can hit all of South Korea and most of Japan as well as its artillery batteries posted close to its border with the South. Jane's Defence estimated the North could rain 500,000 shells an hour into the Seoul area, which is home to about half of South Korea's 49 million people.

A North Korean first strike with artillery and rockets, which may also carry biological weapons or material to spread radiation poisoning, would cause major damage to economic powers South Korea and Japan, which in turn would deal a heavy blow to the global economy. It would also be a suicidal move, because the U.S.-led counter-strike would quickly destroy the country.

WHAT ARE NORTH KOREA'S NUCLEAR FACILITIES?

The heart of the North's nuclear arms programme is the Yongbyon nuclear plant, located about 100 km (60 miles) north of the capital Pyongyang. Its key facilities are a plant that makes nuclear fuel, an antiquated reactor that burns the fuel and a plant that separates plutonium from spent fuel. The North has various other clandestine facilities where it works on weapons designs and uranium enrichment, intelligence source said.

WILL DIPLOMACY WORK TO END THE NORTH'S NUCLEAR PROGRAMME?

Probably not.

North Korea for years has used its military threat to squeeze concessions from global powers and experts doubt it will give up its biggest card while leader Kim Jong-il is in charge. For Kim, only nuclear weapons can give his small state real standing in the world. They also underpin his military-first policy in the face of what Pyongyang says is the threat of a U.S. invasion.

HOW BIG OF A THREAT IS PROLIFERATION?

The proliferation threat is real. The United States, under former President George W. Bush, suspected the North aided Syria in building a nuclear programme.

Even though the North's nuclear arms programme is based on what experts consider outdated technology, cash-strapped North Korea has mastered the nuclear fuel cycle and is capable of helping other states make plutonium for weapons. (Editing by Jonathan Thatcher and Dean Yates)

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