South Korean military officials say North Korea has flown five drones across their mutual border. The "unmanned aerial vehicles" violated South Korean airspace in the border areas around Gyeonggi province, said the country"s joint chiefs of staff. One drone flew all the way to the northern edge of the capital, Seoul, before returning across the border. Jets and attack helicopters were deployed, but 100 rounds fired from helicopters failed to shoot them down. A South Korean military official said they had since lost track of all the drones, but that they were no longer in flight. The incursion comes amid increased tensions on the Korean peninsula, with the North conducting a record number of missile tests this year. The drones were spotted crossing the border at about 10:30 local time (01:30 GMT). One of the South Korean warplanes involved in the operation, a KA-1 light attack aircraft, later crashed, but its two pilots escaped unhurt. The plane fell to the ground in Hoengseong County, east of Seoul, soon after takeoff from an air base in the nearby city of Wonju, according to the air force, quoted by Yonhap. South Korea also suspended planes taking off and landing at its Incheon and Gimpo airports for about an hour. A South Korean military official described the latest incursion as a clear act of provocation by Pyongyang. "Our military will continue to respond thoroughly and resolutely to North Korea"s provocations," the military added. In response, the South Korean military said it also sent surveillance planes into the North to photograph its military installations. The last time a North Korean drone crossed the border was five years ago in June 2017, when tensions between the two Koreas were last at their highest. North Korea"s drones pose a threat to South Korea"s security as they could be used both to spy on the South and to launch an attack on it. Earlier this month, the North claimed to have performed major tests needed to help it develop its first spy satellite, which could be used to monitor South Korea. It released an aerial photo of Seoul, which it said had been taken during the test. Experts believe North Korea is working to refine and improve its weapons, while putting pressure on the United States to ease sanctions in any future negotiations. — BBC