SEOUL (AFP) - Communist North Korea has completed deployment of new medium-range missiles and expanded its military to 1.2 million, South Korea said Monday, calling the threat from its neighbour "direct and serious." The intermediate-range missiles can travel up to 3,000 kilometres " enough to cover most of Asia " and carry a warhead of up to 650 kilograms (1,430 pounds), Seoul's 2008 defence white paper said. The document was published as the North steps up threats against the South and continues apparent preparations to launch its longest-range missile. "North Korea's developing and reinforcing of conventional weaponry, as well as the weapons of mass destruction like nuclear and missiles, and the frontline deployment of military power are a direct and serious threat to our security," the document said, using stronger language than in the last paper in 2006. It did not say how many medium-range missiles the North has "deployed for operational use" since 2007. The paper said the overall size of the military had grown by 20,000 to 1.19 million since 2006, but the number of lightly equipped special forces trained swiftly to infiltrate South Korea had increased 50 percent to 180,000. "After examining the wars in Iraq and Afghanistan, North Korea appears to have developed new strategies that can complement its shortfalls while reinforcing its strengths," said Shin Won-Sik, deputy for policy planning at the defence ministry. "Their aim appears to blur the line between friend and foe once a conflict erupts," Yonhap news agency quoted him as saying, suggesting the North would wage guerrilla warfare to compensate for a lack of advanced weaponry. "North Korea deems it very important to be able to quickly cause disarray among its enemies," Shin told a briefing. Pyongyang has expanded the warhead capacity of its short-range missiles by 170 to 200 kg across the board over the past few years, the white paper said. It had increased the number of its multiple rocket launchers by 300 over two years to about 5,100 and reinforced its submarines. The paper reiterated a 2006 assessment that North Korea possesses 2,500 to 5,000 tonnes of chemical weapons. It said the North is "presumed" to have secured about 40 kg of bomb-making plutonium from reprocessing spent nuclear fuel rods at its Yongbyon reactor on three occasions in the past. However, it dropped an earlier reference to the presumed manufacture of one or two nuclear bombs " an apparent attempt to deny the North, which carried out an atomic test in 2006, the status of a nuclear power. Pyongyang is angry with Seoul's conservative President Lee Myung-Bak, who has scrapped a policy of largely unconditional aid and engagement. It has cancelled all peace accords with Seoul and state media has warned of war. US and South Korean officials have also said the North is preparing to test-fire its longest-range missile, the Taepodong-2, which has an estimated range of 6,700 km that puts Alaska within striking distance. Pyongyang first tested the Taepedong-2 in 2008 but it blew up after just 40 seconds. "North Korea is a substantial, not symbolic, threat to us (South Korea)," said Baek Seung-Joo of the Korea Institute for Defence Analyses. "The special warfare forces, if combined with North Korea's chemical weapons, could not only inflict substantial damage on us but also drive South Korea into panic quickly," he told AFP. US Secretary of State Hillary Clinton, in strong comments Friday in Seoul, warned the North to stop provocation and said its war of words with the South would not help it forge a new relationship with Washington. She said any missile test would breach a UN resolution and urged Pyongyang to comply with a six-nation nuclear disarmament pact.