According to the South Korean Joint Chiefs of Staff, "the traces of flight by an unidentified object" were detected over the Demilitarized Zone on Monday. However, there were no further reports on the issue.
The report comes just a day after US President Donald Trump arrived at the DMZ, where he met with North Korea's Chairman Kim Jong-un. Trump briefly entered North Korean territory, and later noted he may invite Kim to the US.
The border barrier and the Demilitarized Zone between North and South Korea were established in 1953. The DMZ is 250 kilometres (160 miles) long, and about 4 kilometres (2.5 miles) wide. During the last few years the tensions on the border have subsided with both countries dismantling their "frontline" guard posts and resuming Inter-Korean railroad transportation.