(Yonhap) -- South Korea and the United States are conducting a joint study on Seoul's own missile defense system amid high tensions following North Korea's two deadly attacks last year, sources said Friday.

   South Korea is aiming to complete the building its own missile defense system by 2015 that is designed to intercept ballistic missiles from North Korea.

   South Korea, which has ruled out joining the U.S.-led global missile defense system, has gradually built the independent, low-tier missile defense shield since 2006 by acquiring Patriot missiles and long-range early warning radars.

   The Korea Air and Missile Defense (KAMD) system is aimed at allowing the South's military to track and intercept incoming ballistic missiles and cruise missiles from North Korea.

   "Defense research institutes from both countries signed an agreement on a joint study on the KAMD in September last year," said an official at the defense ministry. "Based on the agreement, both sides are conducting a joint study."

   The missile defense system is part of the military's mid-term plans to bolster its defense capabilities against North Korea's focus on unconventional, or "asymmetric," warfare, the sources said.

   With the help of ship-to-air missile systems from Aegis-equipped destroyers and modified Patriot Advanced Capability-3 (PAC-3) interceptors, the KAMD system would enable the South's military to engage the North's low-flying, short- and medium-range missiles, they said.

   North Korea has deployed hundreds of short-range Scud missiles with a range of up to 500 kilometers. The North succeeded in test-firing Rodong missiles with a range of 1,300 kilometers in the 1990s and also deployed them for operational purposes, according to the defense ministry.

   In 2006, North Korea test-launched a long-range Taepodong-2 missile, but it exploded 40 seconds after launch. Another Taepodong-2 traveled some 3,200 km and landed in the Pacific Ocean in 2009.

   Tensions on the Korean Peninsula remain high after North Korea torpedoed a South Korean warship and shelled a southern border island last year, resulting in a total of 50 people, including two civilians, being killed.

   The defense ministry said last month that South Korea will deploy advanced spy drones and stealth fighter jets at an early date. South Korea had originally planned to introduce the unmanned spy drones by 2015.