A day after the US used nuclear-armed B-52 bombers in joint military drills with South Korea; the North Korean army issued a warning that it would attack US military bases in Japan and the island of Guam in the Pacific if provoked.

Pyongyang condemned the use of B-52 bombers, terming the flights as an "unpardonable provocation." The country also threatened military action in case the flights continue. Pyongyang insisted that the flights were a rehearsal for invasion.

A spokesperson for the North Korea's supreme army command said that if the enemy threatens North Korea with nuclear weapons, they would respond with tougher nuclear attacks.

In response to the flights, the spokesperson said, "We cannot tolerate the US carrying out nuclear strike drills. the US should not forget that the Andersen base as well as naval bases at Japan's main island and Okinawa, are all within the range of our precision target assets."

The US confirmed the use of the B-52 bombers, which took off from its Andersen Air Force base in Guam and flown over South Korea, but insisted that the flights were a part of the two country's annual joint exercises.

The US however added that it had publicized the bombers' use this time to highlight its commitment to defend its ally South Korea.

Tensions between North Korea and the US are at their peak for several years. Last month, UN imposed sanctions on North Korea after it conducted nuclear tests.