South Korea and Japan should bolster their defense ties in response to growing threats from North Korea, Japan's defense minister said, citing advances in the North's missile development.

Japan believes North Korea's missiles could have a range of more than 10,000 kilometers, Gen Nakatani said, making them capable of striking targets in South Korea, Japan and the U.S. mainland.

"Assuming that a warhead weighs under 1 ton, we presume that it will be possible for (the missiles) to have a range exceeding 10,000 km and carry a warhead weighing about 200 kilograms," the minister told Yonhap News Agency in an exclusive interview at his office on Tuesday.

North Korea is also believed to have mastered the technology to improve its missiles' range and precision, he added.

On Jan. 6, North Korea conducted its fourth nuclear test before launching a long-range rocket on Feb. 7, which the outside world views as a banned test of ballistic missile technology.

Although it's unlikely that the nuclear test was of a hydrogen bomb, as the North claims, the communist country may have detonated one on a small scale and succeeded in miniaturizing nuclear weapons to fit atop missiles, he said.

Citing such developments, Nakatani called for stronger defense cooperation among South Korea, Japan and the U.S. In particular, Seoul and Tokyo should sign a pair of defense deals, known as the General Security of Military Information Agreement and the Acquisition and Cross-Servicing Agreement, he said.

"Through the GSOMIA, the two countries can share their valuable information and better ensure each other's safety," he said. "It's important to lend goods to each other when one is in trouble."

A previous attempt to sign the GSOMIA was scrapped in 2010 amid strong backlash from the South Korean public over the way the government handled the deal. South Koreans still harbor deep resentment and suspicions toward Japan because Tokyo ruled the Korean Peninsula as a colony from 1910-45.

Nakatani said he stressed the importance of intelligence sharing between the two nations during a recent phone conversation with South Korean Defense Minister Han Min-koo.

Addressing South Korean concerns that Japan's exercise of its right to collective self-defense may lead to Japanese troops entering the Korean Peninsula, Nakatani said, "Regarding the Korean Peninsula, it's only natural to act after seeking South Korea's understanding and approval."

"Japan and South Korea are countries that share the same values, such as liberalism and democracy," he noted, suggesting there should be more joint military drills and exchanges of defense personnel. (Yonhap)