A South Korean report claims that North Korea has deployed a new type of ballistic missile capable of reaching the US Pacific territory of Guam.
The defense ministry report, released on Monday, said the new missile has a range of at least 3,000km and has been deployed "recently".
The reported striking range of the missle would reach Guam, the northern tip of Australia, much of Russia and India.
The ministry report also said the North began developing the missile in the late 1990s, but did not offer further details, including how many have been deployed.
The report comes as the North is believed to be preparing to test-fire its most advanced missile, the Taepodong-2, which is allegedly capable of reaching Alaska.
South Korea also claims the North is "presumed" to have secured about 40kg of atom bomb-making plutonium from reprocessing spent nuclear fuel rods from its Yongbyon reactor.
Pyongyang carried out its first atomic test in October 2006, but it is not known whether it could manufacture a nuclear warhead.
Army size 'increase'
The report also claims that the size of the North Korean military had grown to 1.19 million, an increase of 20,000 from 2006, while the number of its lightly-equipped special forces trained to infiltrate South Korea had increased 50 per cent to 180,000.
Monday's published assessment came amid mounting tensions between the two countries, which are still technically at war since the 1950-1953 Korean conflict ended only in an armistice.
The North is angry with the government of Lee Myung-Bak, South Korea's president, who has scrapped a policy of largely unconditional aid and engagement.
It has cancelled all military and political agreements with Seoul, including one recognising their disputed sea border as an interim frontier.