June 18 (UPI) -- North Korea's military appeared to be moving to the front lines near the South as a U.S. reconnaissance plane flew over the peninsula, following days of threats and provocations from Pyongyang.
Sources in the South Korean military said North Korean troops were stationed on the North's side of the Korean demilitarized zones, at vacated guard posts of the tense border, South Korean news service News 1 reported Thursday.
South Korean military sources said the mobilization of North Korea's armed forces appear to be a follow-up measure after a declaration from Pyongyang's army.
The Korean People's Army had said it would be deploying its "No. 1" combat operations system, including logistics needed to supply troops.
"We are keeping an eye on related activities of the North Korean military," a source with Seoul's joint chiefs of staff told News 1. "So far, no direct [military] action has been confirmed."
The South Korean source said "it is true" there was forward deployment to North Korean guard posts, but no other measures have been taken by Pyongyang.
On Wednesday North Korea had said it would retake vacated guard posts and take military action if North Korean defectors in the South continued to send anti-Pyongyang leaflets by helium balloon.
North Korean movements have also been detected at the disputed Northern Limit Line that divides North and South in the West Sea, or Yellow Sea.
North Korea's army could be on the move as the United States deploys the RC-135W, Rivet Joint, to the peninsula on Thursday, according to Aircraft Spot, an aviation tracker.
Two Air Force B-52H bombers also trained with F-15 fighter jets of Japan's Air Self-Defense Forces on Wednesday, the U.S. Air Force said Thursday.