Seoul, Jan 6 (IANS/EFE): South Korea believes its Communist neighbour has already acquired a "significant" level of technology to miniaturise nuclear warheads and put them on its missiles, according to a defence white paper published Tuesday.

"North Korea is presumed to have secured some 40 kg of weapon-grade plutonium by reprocessing spent nuclear fuel multiple times, and it is evaluated to be working on a highly enriched uranium programme," it added.

Although Pyongyang is yet to display its miniaturising capabilities, South Korean and US experts and officials believe that North Korea already has the technology to do so.

"We don't have any intelligence that North Korea completed the miniaturisation," a South Korean defence ministry spokesperson told the Yonhap news agency.

"But eight years have passed since North Korea carried out its first nuclear test in 2006. Pyongyang's miniaturisation of nuclear weapons appears to have reached a significant level," he explained.

The white paper also said that the North was "presumed to have (missile) capabilities that could threaten the US mainland, having fired off long range missiles five times."

North Korea is believed to have long range missiles with a range of some 10,000 km, which makes both countries an easy target.