The South Korean Joint Chiefs of Staff said the allies had launched ATACMS surface-to-surface missiles at targets in the East Sea, also known as the Sea of Japan.
The 10-minute volley comes a day after Pyongyang launched eight short-range ballistic missiles following joint US-South Korea exercises that mobilized an aircraft carrier.
“Our army strongly condemns the series of provocative ballistic missiles and strongly urges to stop the acts that increase military tensions on the peninsula,” he added.
The US Indo-Pacific Command said one US and eight South Korean missiles were launched from northeastern South Korea during the exercise to demonstrate their ability to “rapidly respond to times of crisis.”
The communist regime has accelerated its weapons development program this year, despite economic sanctions against it.
Senior South Korean and US officials as well as analysts believe that the country led by Kim Jong Un is preparing to conduct a nuclear test.
Monday’s shooting is the second joint show of force between Seoul and Washington since the arrival of new South Korean President Yoon Suk-yeol, who advocates a tougher stance against Pyongyang.
“Our government will respond firmly and severely to any provocation from North Korea,” Yoon said Monday.
Last month, both countries launched missile launches after North Korea fired three ballistic missiles, including one with an alleged intercontinental range.