Two supersonic U.S. bombers flew over South Korea on Wednesday — with one landing on the Korean Peninsula for the first time in 20 years — amid soaring tensions after the North's fifth nuclear test on Sept. 9.

The U.S. B-1B landed at Osan air base 40 km (25 miles) south of the capital, the air force said in a statement. It said the flight, which took off from Andersen Air Force Base in Guam, was the closest a B-1B strategic bomber had ever flown to the border between South and North Korea.

South Korea's Yonhap news agency reported that the aircraft flew over a U.S. live-fire training site in the Pocheon area bordering the North.