The missiles flew around 250 kilometers before falling into the Sea of Japan, also known as the East Sea, South Korea's Yonhap news agency reported, citing the country's Joint Chiefs of Staff.

The US Pacific Command also confirmed the launches, saying they posed no immediate threat to US personnel or territory, or to US allies.

There was initially no reaction from Pyongyang.

At the start of the five-day military exercise south and east of the South Korean island of Jeju on Monday, North Korean Defense Minister Kim Song Gi described the drills as "provocative."

The exercise involved the air forces and navies of the three countries. According to the United States, it was held in international waters.

North Korea had fired several short-range missiles towards the Sea of Japan around three weeks earlier.

Pyongyang is barred from launching ballistic missiles under several United Nations Security Council resolutions.

In mid-August, both South Korea and the United States made significant concessions to North Korea.

US President Donald Trump ordered a major scaling-back of a joint military exercise with South Korea, citing what he called his "very good relationship" with North Korean leader Kim Jong Un.

Trump said he expected to meet Kim again later this year. Kim has so far not publicly responded to the offer of talks.

Last week, Kim said he wanted to further develop North Korea's navy into a nuclear-armed force.