SEOUL (Reuters) – The United States deployed a B-52 bomber on a low-level flight over its ally South Korea on Sunday, a show of force following North Korea’s nuclear test last week. North Korean leader Kim Jong Un maintained that Wednesday’s test was of a hydrogen bomb and said it was a self-defensive step against a U.S. threat of nuclear war. North Korea’s fourth nuclear test angered both China, its main ally, and the United States, although the U.S. government and weapons experts doubt the North’s claim that the device was a hydrogen bomb. The massive B-52, based in Guam and capable of carrying nuclear weapons, could be seen in a low flight over Osan Air Base at around noon. It was flanked by two fighter planes, a U.S. F-16 and a South Korean F-15, before returning to Guam, the U.S. military said in a statement. Osan is south of Seoul and 77 km (48 miles) from the Demilitarized Zone that separates the two Koreas. The flight was “in response to recent provocative action by North Korea,” the U.S. military said. In Washington, White House Chief of Staff Denis McDonough said on Sunday the flight underscored to South Korea “the…