The U.S. military in South Korea plans to bring in precision-guided "Excalibur" shells capable of striking artillery batteries in North Korea by the end of the year, a military source said Thursday.

The U.S. 2nd Infantry Division and South Korea's Agency for Defense Development successfully conducted a test-firing of the Excalibur shell in May, the source said. The U.S. forces also plan to additionally deploy Patriot-3 missiles and ATACMS surface-to-surface missiles, the source said.

GPS-guided Excalibur shells are fired from 155mm guns, such as the Paladin artillery system, and are considered good for striking artillery batteries behind mountains as it strikes targets vertically.

North Korean artillery is a major threat to South Korea. In November 2010, the communist nation shelled the South's border island of Yeonpyeong near the tense Yellow Sea border between the two sides, killing four people, including two civilians.

Other weapons the South Korean and U.S. militaries possess to cope with North Korean artillery threats include satellite-guided Joint Direct Attack Munitions (JDAMs), GBU-24 air-to-ground guided missiles and Korean Global Positioning System-guided Bombs (KGGBs).

The United States keeps 28,500 troops in South Korea to deter North Korean aggression, a legacy of the 1950-53 Korean War that ended in a truce, not a peace treaty, which means the divided peninsula is still technically at war.