The United States on Sunday flew a massive B-52 warplane over South Korea, claiming the show of strength in response to North Korea’s nuclear test last week. White House Chief of Staff Denis McDonough said the flight reiterated "the deep and enduring alliance” the US has with South Korea, Reuters reported.

The B-52, which is based in the US-controlled island of Guam, can carry nuclear weapons and was seen flying low over the Osan Air Base flanked by two fighter jets. Osan is south of Seoul and 77 kilometres from the area that separates the two Koreas.

North Korean leader Kim Jong Un had claimed that the country had tested a hydrogen bomb on Wednesday, in a move that angered its main ally China and raised concern all over the world. The US however has expressed doubts over whether it was a hydrogen bomb or not. The US had flown B-52s in response to North Korea's nuclear operations in 2013 as well.