A North Korean ballistic missile landed less than 60 kilometers off South Korea's coast on Wednesday, prompting South Korea to launch missiles in protest, Reuters reported.

The missile landed outside of South Korea's territorial waters, but south of the Northern Limit Line (NLL), a disputed inter-Korean maritime border in what South Korean President Yoon Suk-yeol called an "effective act of territorial encroachment."

South Korean warplanes fired three air-to-ground missiles into the sea north across the NLL in response, the South's military said.

The South's launches came after Yoon's office vowed a "swift and firm response" so North Korea "pays the price for provocation."

The North Korean weapon was one of three short-range ballistic missiles fired from the North Korean coastal area of Wonsan into the sea, South Korea's Joint Chiefs of Staff (JCS) said. The JCS later said as many as 10 missiles of various types had been fired from North Korea's east and west coasts.

The JCS said at least one of the missiles landed 26 kilometers south of the NLL, 57 kilometers from the South Korean city of Sokcho, on the east coast, and 167 kilometers from the island of Ulleung, where air raid warnings were issued.

The launches came just hours after Pyongyang demanded that the United States and South Korea stop large-scale military exercises, saying such "military rashness and provocation can be no longer tolerated."

Despite Yoon's declaring a national week of mourning after more than 150 people were killed in a weekend crowd surge in Seoul, the United States and South Korea began one of their largest combined military air drills on Monday. Dubbed Vigilant Storm, the exercises involve hundreds of warplanes from both sides staging mock attacks 24 hours a day.

North Korea had said that a recent flurry of launches were in response to allied drills.

Pak Jong Chon, secretary of the Central Committee of North Korea's ruling Workers' Party, said in a statement on Wednesday that the number of warplanes involved in Vigilant Storm proved the exercise was "aggressive and provocative" and specifically targeted North Korea. He said even its name imitated the U.S.-led Operation Desert Storm against Iraq in the 1990s.

"The hostile forces' inordinate moves for military confrontation have created a grave situation on the Korean peninsula," Pak said in a statement carried by state news agency KCNA.

A spokesman for the South Korean military said authorities were analyzing the launches to see whether the missiles' flight paths were intentional or whether one had gone off course.

Japan defense minister Yasukazu Hamada said the government believed at least two ballistic missiles had been launched from North Korea, one flying east and another southeast.

It was the first time a North Korean ballistic missile had landed near South Korean waters, JCS said.

"Our military can never tolerate this kind of North Korea's provocative act, and will strictly and firmly respond under close South Korea-U.S. cooperation," JCS said in a news release.

North Korea's actions threaten the peace and stability of Japan, the wider region, as well as the broader international community, and are utterly unacceptable, Hamada said.

Japan has lodged a complaint and protested the actions via diplomatic channels in Beijing, he added.