Two US strategic bombers have been spotted near the Korean Peninsula, a flight tracker said Friday, amid heightened tensions after North Korea threatened South Korea over the sending of anti-Pyongyang leaflets.

The two B-52Hs were seen flying over northern Japan on Friday, according to Aircraft Spots. It did not provide other details such as exactly when the bombers were spotted.

This marked the second time that the heavy bombers have flown near the Korean Peninsula this week. Two B-52Hs participated in a joint drill on Wednesday with Japan over the East Sea, according to the US Pacific Air Forces.

The US sent the bombers amid heightened tensions after North Korea repeatedly threatened a series of retaliatory steps against South Korea over its failure to prevent activists from sending anti-Pyongyang leaflets into the communist state.

North Korea blew up a liaison office in its border town of Kaesong on Tuesday. It also threatened to send troops to border regions and reestablish guard posts removed from the Demilitarized Zone separating the two Koreas.

On Wednesday, an aviation tracker said that an aircraft used by North Korean leader Kim Jong-un flew from Pyongyang to the eastern part of the country, sparking speculation that he could have gone to the east coast for provocative events, such as the launching of a new ballistic missile submarine. (Yonhap)