North Korea on Monday fired two short-range ballistic missiles into the East Sea, apparently to protest South Korea-U.S. military drills, according to Seoul’s Defense Ministry.

Seoul called the move a “provocative action” that further raised military tensions on the peninsula and violated a series of U.N. Security Council resolutions prohibiting any launch using ballistic missile technology.

The North fired four ballistic missiles last Thursday and four “KN-09” rockets into the East Sea about a week earlier. One of its patrol boats also crossed the Northern Limit Line, a de facto sea border, three times between last Monday and Tuesday.

“The missile launch is a provocative action that poses a grave threat to the international aviation order and the safety of civilians given that it was an abnormal military action that took place without any prior notice or warning,” said Seoul’s Defense Ministry spokesperson Kim Min-seok during a regular briefing.

“Pyongyang shows contradictory attitudes ― upping its peace offensive on the surface while conducting reckless provocative moves. We send the North a grave warning against such moves and strongly call on it to immediately cease them.”

The missiles were launched from Wonsan in the North at around 6:19 a.m. and fell into the sea after having flown some 500 kilometers, officials said. The missiles are presumed to be the Scud-C, with a range of 500 km, or the Scud-ER, an upgraded version of the Scud-D with a range of 700 km, they said.

A Seoul official said the two ballistic missiles landed within Japan’s air defense identification zone, noting that the launching of the missiles without setting a no-sail zone runs afoul of international obligations.

“Both of the missiles flew past South Korea’s ADIZ and fell in Japan’s ADIZ. The North fired missiles into areas where civilian aircraft and vessels pass through,” the official said, declining to be named.

The Defense Ministry spokesperson noted that the missile launch appeared to have contravened U.N. Security Council Resolutions 1874, 2087 and 2094, which ban Pyongyang from conducting ballistic missile launches.

Following Pyongyang’s recent saber-rattling, South Korea and the U.S. have strengthened their monitoring activities and readiness posture, the spokesperson said.

“We are keeping close tabs on the North Korean military’s movements. We are also ready to sternly respond to any provocations,” Kim said.

The allied Key Resolve command post exercise began on Feb. 24 and will end on Thursday. The allies will also hold the Foal Eagle field exercise, which will run through April 18.

Pyongyang has repeatedly demanded that the annual exercises be called off. It has argued that the drills are a rehearsal for a “nuclear war of invasion,” while Seoul has argued that the drills are entirely defensive in nature.

By Song Sang-ho (sshluck@heraldcorp.com)