SEOUL, Jan. 11 (Xinhua) — South Korea's defense white paper estimated the Democratic People's Republic of Korea (DPRK) may hold 50 kg of plutonium, which can produce 10 nuclear warheads based on its technology.

The DPRK's plutonium holdings increased by 10 kg in the past two years to 50 kg, Seoul's defense ministry said in its biennial defense white paper released on Wednesday.

The white paper said Pyongyang secured the plutonium by reprocessing spent nuclear fuel rods several times and that its highly-enriched uranium (HEU) program has advanced to a significant level.

The defense ministry first unveiled the white paper in 1967, and has since published the defense report every two years to explain security situations on the Korean Peninsula and its defense policy, according to the press release.

Some of local media outlets speculated that the 10-kg increase in the DPRK-owned plutonium might have been exaggerated given that Pyongyang conducted its fourth and fifth nuclear tests in January and September. A nuclear test is known to cost the DPRK four kg of plutonium.

Top DPRK leader Kim Jong Un said in his new year speech that his country entered a final stage in preparations to test-launch a long-range ballistic rocket. The January nuclear detonation was followed by the launch of a long-range rocket.

The DPRK's regular forces were estimated little changed at about 1.28 million, including 1.1 million army troops, 110,000 air force soldiers, 60,000 navy forces and the new group of 10,000 strategic forces, which were believed to be launched to increase nuclear and missile capabilities.

About 70 percent of DPRK army soldiers are being deployed in the southern part of the country. The DPRK army has about 4,300 tanks and 2,500 armored vehicles as well as 8,600 field guns and 5,500 multiple rocket launchers.

The DPRK air force owns around 1,630 combat aircraft, while the navy has some 70 submarines, according to the white paper.

Meanwhile, the white paper provided separate supplements to explain about Terminal High Altitude Area Defense (THAAD), which Seoul and Washington agreed in July last year to deploy in South Korean soil by the end of this year.

Suspicion has been raised here about the THAAD's capability to intercept DPRK missiles, which fly at an altitude of less than 40 km, as the U.S. missile shield is designed to shoot down incoming missiles at an altitude of 40-150 km.

The THAAD battery, which is to be installed in southeastern South Korea, is incapable of defending the capital city Seoul and its suburban metropolitan area, which accommodate over half of its total 50 million population.

The white paper said the U.S. Patriot interceptors would be more effective than the THAAD to shoot down DPRK missiles targeting the metropolitan area, partly acknowledging the incapability of the U.S. missile defense system on the Korean Peninsula.

The white paper also explained about the signing of the agreement between South Korea and Japan to exchange military intelligence on the DPRK's nuclear and missile programs. It was formally inked on Nov. 23, 2016.

The signing caused strong backlashes here from the parliament and the general public as Japanese Prime Minister Shinzo Abe disclosed his ambition to make Japan a war-waging country by revising its pacifist constitution.

Abe has yet to make sincere apology and acknowledge legal responsibility for past atrocities during the 1910-45 Japanese colonization of the Korean Peninsula.

Japan has claimed its territorial sovereignty over the Dokdo islets, called Takeshima in Japan, which South Korea retrieved after its liberation from the Japanese colonization.

The white paper said South Korea will sternly deal with Japan's territorial claims and history distortion, expressing concerns about Japan's military ambition.