Talks with representatives of six countries aimed at ending North Korea's nuclear development resulted in an agreement to supply more than 100,000 tons of heavy fuel oil to Pyongyang.

A military source told Yonhap that South Korean and U.S. intelligence officials have seen a "sharp increase in the North's winter (military) maneuvering" and suspect the oil aid was being used to fuel military tanks and jets.

North Korea's military exercises could be in response to a scheduled U.S.-South Korean military exercise scheduled to take place in March, an official told Yonhap.