The defense ministry on Thursday ruled out South Korea's participation in the American-led missile defense system, saying it will focus on developing its own program to defend itself from North Korea's missile threats.

Whether to join a U.S.-led missile defense system involving ground-based interceptors and the X-band radar has been a prickly issue in South Korea, as it could spur a regional arms race involving China and further contribute to mounting costs in the national missile program.

The issue has resurfaced after U.S. President Barack Obama on Tuesday said during a joint conference with South Korean President Park Geun-hye that the two countries agreed to jointly invest in missile defenses and shared capabilities against the threat of North Korea.

In response to local reports that Obama's remark may indicate ongoing discussions over Seoul's participation in the American-led missile shield, the South Korean defense ministry said the military has already been cooperating with U.S. forces on missile defense, but the scope is only limited to intelligence sharing.

"South Korea has its own missile defense system for uses against missiles in the terminal stage, which is best suited for countering growing North Korean missile threats," ministry spokesman Kim Min-seok said. "Under the current circumstances, we have cooperated with the U.S. missile defense system for intelligence sharing and are seeking ways to develop the cooperation."

Although Seoul is not opposed to the U.S. program, Kim said the two sides have been working together to monitor and trace North Korea's missiles without establishing additional installations.

"(South Korea and the U.S.) have cooperated with each other to trace North Korean missiles with available resources," Kim said, denying installation of advanced missiles and radars tied to the American system.

South Korea has gradually been building an independent, low-tier missile shield called the Korea Air and Missile Defense System (KAMD) since 2006 by acquiring Patriot missiles and long-range early warning radar.

The KAMD involves an early warning radar as well as ship-to-air and land-based missile defense systems, arming Seoul with the ability to track and shoot down the North's low-flying, short- and medium-range missiles, with help of U.S. early warning satellites.

Seoul has been pushing to bolster its defenses against North Korea, which is believed to have over 1,000 missiles with varying capabilities, but the mid-term plan has taken on new urgency after the communist country successfully fired off a long-range rocket last December.

Pyongyang claims the launch was aimed at sending a working satellite into space, but Seoul and Washington consider it to have been a covert test of its ballistic missile technology.

South Korea currently operates Patriot Advanced Capability

(PAC-2) batteries, which can hit an incoming missile at an altitude of up to 30 kilometers. 

In late April, the South Korean military approved the plan to upgrade the PAC-2 system to the PAC-3 version and buy additional rounds. PAC-3 interceptors provide back-up protection as the missile returns to earth.

The U.S. military has been operating a four-stage program that uses sea-based, as well as land-based ballistic-missile interceptors since 2009.

Several foreign navies are participating in sea-based ballistic missile defense jointly with U.S. forces, including Japan and Australia.

In response to Pyongyang's threat to strike the U.S. with its missile and nuclear weapons against South Korea-U.S. drills in April, the Pentagon stationed 14 missile interceptors in Alaska to protect the U.S. west coast from North Korea.

The Pentagon also positioned two Aegis guided-missile destroyers in the western Pacific and a Terminal High Altitude Area Defense (THAAD) missile defense system in Guam. (Yonhap News)