Seven were fired by South Korea and one by the US, according to the South Korean Joint Chiefs of Staff, which said they demonstrated that "even if North Korea provokes with missiles from multiple locations, (South Korea and the US have) the ability and readiness to immediately strike with precision."
North Korea fired eight short-range ballistic missiles from multiple sites in the country into waters east of the Korean peninsula on Sunday, according to the Joint Chiefs of Staff, who called the actions a "serious provocation that harms peace and stability of not only the Korean peninsula but also the international community."
The president vowed to respond "firmly and sternly" to North Korean provocations during a speech marking South Korea's Memorial Day on Monday.
North Korea's launch on Sunday is its third missile test since the start of Yoon's term and the 17th this year.
Pyongyang's previous launch occurred on May 25 as US President Joe Biden was returning to the US after a trip to Asia. Biden's trip included a stop in Seoul during which the American President and his South Korean counterpart agreed to begin discussions on restarting and potentially expanding joint military drills that had been halted under his predecessor Donald Trump.
The US and South Korea also fired missiles in response to the May 25 North Korean missile launch. Including Monday's launch, South Korea has fired back three times this year, after a hiatus since 2017.
On both sides, the missile launches are seen as a show of force and are not aimed at specific targets. Typically the missiles land in the sea.
The latest North Korean launch came a day after the navies of South Korea and the US concluded a three-day combined exercise in the waters off Japan's Okinawa, South Korea's military confirmed to CNN.
Japanese Prime Minister Fumio Kishida also "strongly protested" the latest North Korean launch, telling reporters Sunday that it was a clear violation of UN resolutions, while Defense Minister Nobuo Kishi called it "unprecedented" and confirmed at least six, but possibly more, missiles fired by North Korea had fallen outside Japan's Exclusive Economic Zone.
On Sunday, the US Armed Forces and Japan Self Defense Forces also held a joint drill following North Korea's multiple missile launches, the US Indo-Pacific Command Public Affairs department said.
The US and Japanese forces held a "bilateral ballistic missile defense exercise" to "demonstrate the readiness of the US-Japan alliance to respond to regional threats," it said.
The Japan Joint Staff said the exercise reaffirmed the readiness of both forces, "demonstrating the close cooperation between Japan and the United States in addressing the ballistic missile threat, and further strengthening the Japan-US alliance."
CNN's Blake Essig and Emi Jozuka in Tokyo contributed to this story.