South Korea on Monday held a joint air power exercise with the United States in its airspace involving B-1B strategic bombers, a South Korean Defense Ministry spokesman said Tuesday.

(South Korean Defense Ministry)

The exercise with the U.S. bombers was harshly criticized by North Korea, which announced the same day that it had successfully test-fired a ballistic missile in defiance of international warnings.

Spokesman Moon Sang Gyun confirmed the drill during a press briefing, but declined to provide further details.

A South Korean government source told Yonhap News Agency that two B-1Bs arrived in the airspace over the East Sea at around 10:30 a.m., five hours after the North test-fired a short-range ballistic missile.

South Korea refers to the waters, which Japan calls the Sea of Japan, as the East Sea.

The bombers were accompanied by South Korea's F-15K fighter jets during the two-hour unannounced flight near and over the peninsula, the source was quoted by Yonhap as saying.

North Korea's official media, the Korean Central News Agency, said in an English-language report Tuesday that "the U.S. imperialists committed a grave military provocation by letting a formation of infamous B-1B nuclear strategic bombers fly over South Korea once again to stage a nuclear bomb dropping drill."

"Such military provocation of the U.S. imperialists is a dangerous reckless racket for bringing the situation on the Korean peninsula to the brink of a war," KCNA said.

It also said the exercise coincided with the "war drill against the DPRK with the Carl Vinson and Ronald Reagan nuclear aircraft carrier strike groups." DPRK is the acronym of North Korea's formal name, the Democratic People's Republic of Korea.

In a show of force, the United States has sent the aircraft carrier Ronald Reagan to waters off the Korean Peninsula, where a naval strike group led by the aircraft carrier Carl Vinson is already deployed.