North Korean drones that crashed in South Korea two years ago were too poorly built to carry any threatening weapons, a government source said Sunday, citing the results of a close analysis by a South Korean military research agency.

Three unmanned aerial vehicles, or drones, that had crashed were found near the inter-Korean border in March and April of 2014.

The South Korean authorities later announced that the drones all originated from North Korea.

The government source in Seoul said that the Agency for Defense Development has restored the three drones and conducted flight tests with them before concluding that they are incapable of carrying weapons weighing 3 or more kilograms.

"The ADD has successfully restored the three North Korean drones and flown them to gauge their actual performance," the official said.

"The drones failed to carry weapons weighing 3 to 4 kilograms. Instead they were only able to carry a grenade-level object weighing 400 to 900 grams."

He added that engines and cameras found in the North Korean drones were all low-grade and built in the 1980s.

Despite their poor quality, however, the North Korean drones are hard for radars to detect, the official said, adding that the South Korean military's relevant radar system is being reinforced to deal with the problem. (Yonhap)