Kim Yo-jong, North Korean leader Kim Jong-un's sister and currently vice department director of the ruling Workers' Party's Central Committee in this file photo. (Yonhap)

SEOUL – North Korea fired two "strategic cruise missiles" from a submarine in waters off its east coast over the weekend, the country's state media said Monday.

The North's first known firing of cruise missiles from a submarine is widely viewed as an apparent show of force against a major South Korea-U.S. combined military exercise.

The missiles were fired from the 8.24 Yongung in waters off Kyongpho Bay in the East Sea in an underwater launching drill held at dawn Sunday, according to the official Korean Central News Agency (KCNA).

"The drill confirmed the reliability of the weapon system and examined the underwater-to-surface offensive operations of submarine units that constitute one of other major forces of the DPRK nuclear deterrent," the KCNA said in an English-language report, using the acronym of the North's official name.

The missiles precisely hit preset targets in the East Sea after "traveling the 1,500 km-long eight-shaped flight orbits" for 7,563 to 7,575 seconds."

The latest launch came on the eve of the start of the allies' 11-day Freedom Shield exercise, which the North calls "preparations for a war of aggression" against it.

North Korea said its latest underwater launching drill "verified the current operation posture of the nuclear war deterrence means in different spaces."

Earlier in the day, South Korea's military said it detected an unspecified missile launched from a submarine in waters off the North's eastern coastal city of Sinpo on Sunday morning.

It did not immediately provide other details.

"While strengthening its monitoring and vigilance, our military is maintaining a full readiness posture in close cooperation with the U.S.," the Joint Chiefs of Staff said in a text message sent to reporters.

Cruise missiles fly low and maneuver, making them better at evading missile defenses. The North said last month it launched four "Hwasal-2 strategic cruise missiles."

Military experts assessed the North has improved the striking capability of its submarine.

A cruise missile capable of flying some 1,500 km could put the entire of South Korea and U.S. military bases in Japan within range.

The North is widely expected to conduct further weapon tests to protest the allies' military exercises, as it has threatened to take "unprecedentedly strong" and "overwhelming" counteractions against what it called the U.S. hostile policy.

At a key party meeting presided over by North Korean leader Kim Jong-un on Saturday, the North decided to take "important, practical" measures for the "offensive use" of war deterrents, according to the KCNA.

His younger sister Kim Yo-jong earlier warned the North could turn the Pacific into a "firing range."

Some observers said the secretive nation may launch an intercontinental ballistic missile (ICBM) on a normal angle toward the Pacific. (Yonhap)