South Korea's military fired warning shots after it spotted an unidentified object flying from North Korea across the Demilitarized Zone that divides the two countries, according to the South Korean Joint Chiefs of Staff.
The object, which the South Korean military said was no longer visible, was spotted two days after Pyongyang test-fired a ballistic missile -- its second missile test in seven days.
It's not the first time South Korea has reacted to an object sent across its border.
The South responded with machine-gun fire after an unidentified North Korean aircraft crossed the DMZ early last year. It "immediately went towards the North," a South Korean official said at the time.
North Korea is believed to have a fleet of more than 1,300 fighter jets, as well as an unspecified number of its own unmanned aerial vehicles, according to a 2015 report to Congress from the US Department of Defense.
Two suspected North Korean drones were found in South Korea in 2014, one on the island of Baengnyeong and another in the city of Paju, close to the border.
Actually it was not a UFO but a balloon coming from North Korea. But it seems that the topic you posted has some missing lines, but the said UFO was already been identified and verified by South Korea as a North Korean Propaganda Balloons. Those were the North Korean defector filled balloons with information about the murder of Kim Jong Un's half-brother, Kim Jong Nam.
UFO does not mean a space craft of Aliens or a flying saucer .It can be any object that has not been identified officially..may be a missile or a stealth aircraft or a projectile