SEOUL -?The Republic of Korea (ROK) on Tuesday announced its first official assessment that the long-range missiles of the Democratic People's Republic of Korea (DPRK) may reach the mainland of the United States.

The Defense Ministry said in its biennial Defense White Paper that the DPRK is estimated to have a "capability to threaten the US mainland" after five rounds of test-firing of long-range missiles.

The assessment was based on the DPRK's successful launch of Unha-3 rocket, which is believed to have a range of about 8,000 km, into orbit in December 2012. The previous test-firing failed in April that year.

The DPRK's Taepodong-2 long-range missile has a range of about 10,000 km, according to the white paper.

The paper said the DPRK's capability to miniaturize "nuclear weapons" reached a "significant" level because eight years have passed since its first nuclear test. Pyongyang conducted nuclear tests in 2006, 2009 and 2013.

It marked the first time that South Korea's military uses the word "nuclear weapons" in its white paper.

The paper said the DPRK is estimated to have some 40 kg of plutonium, produced from the 5-megawatt reactor at its main nuclear facility in Yongbyon north of Pyongyang. It was the same estimation as in 2012.

In terms of quantity, the DPRK's military capability got far ahead of the ROK. The DPRK's regular armed forces reach 1.2 million, up about 10,000 in the past two years. It compares with 630,000 military forces in the ROK, down about 9,000 over the past two years.

The DPRK has built up military capability mainly in artillery and warships. It has about 430 warships, up 10 in the past two years and nearly quadruples South Korea's 110 battleships. Its tanks increased from 4,200 to 4,300 units, far outnumbers South Korea's 2,400. It has about 820 fighter jets, more than double South Korea's 400 warplanes.

The DPRK is believed to have founded the 12th Army Corps, raising the number of corps to 10, to strengthen the defense capability in areas bordering China and Russia. The corps was founded in preparation for rising economic cooperation in border regions, including Rajin and Khasan.

The ROK military raised its warning pitch over territorial and historical disputes with Japan. "Regressive perception of history by some Japanese politicians and Japan's unreasonable claim to Dokdo islets are an obstacle to the bilateral relations going future-oriented," the paper said.

The rocky outcroppings, called Dokdo in the ROK and Takeshima in Japan, has long been a source of disputes between the two countries as both laid territorial claim to the islets that lie midway between the two nations.

The ROK has said that Japan illegally incorporated the islets into its territory in 1905 when the Imperial Japan rushed to disseize the Korean Peninsula. The islets have been controlled by the ROK since it stationed border guards there in 1954.

ROK President Park Geun-hye has rejected, since her inauguration in February 2013, to sit face-to-face with Japanese Prime Minister Shinzo Abe, citing his wrong perception of history.

The paper said the ROK military will sternly deal with Japan's unreasonable claim to the Dokdo islets, but it said the military will cooperate with Japan in security issues such as the DPRK's nuclear threats.

ROK, Japan and the United States signed a pact on Dec. 29 to share military intelligence on nuclear and missile threats from the DPRK. Seoul and Tokyo will not exchange intelligence directly, but indirectly only through Washington after consents from both countries.

Meanwhile, the paper forecast that relations between China and the United States will emerge as a core factor for security order in northeast Asia. "Rising China and the US push for the ' rebalance to Asia' strategy will result in the bilateral strategic cooperation and competition, which will act as the most important factor to determine the security in northeast Asia," the paper said.

The paper said that the United States is seeking to implement the "rebalance to Asia" strategy in a successful way while reducing defense budget, adding it reflects the US coordination with its allies and partners.

The US military is known to have around 1.49 million armed forces, 10 aircraft carriers, 72 submarines and 2,224 fighter jets. The US annual defense budget reaches about 600 billion US dollars, higher than Russia's 68 billion dollars and Japan's 51 billion dollars.