North Korea has fired its fifth missile in just five days while US Vice President Kamala Harris is visiting South Korea.
South Korea's military says North Korea fired two ballistic missiles off the east coast.
Ms Harris had her first visit on Thursday to the Demilitarised Zone (DMZ) separating the two Koreas and said the heavily armed border area offered a stark reminder of the "dramatically different paths" the two sides have taken.
In a rare condemnation during a visit to the inter-Korean border, Ms Harris denounced the "brutal dictatorship", illegal arms programme and rampant human rights violations which continue in the North.
South Korea and the United States staged joint naval exercises involving an aircraft carrier in the waters surrounding the Korean peninsula, amid simmering regional tensions over the increased number of missile launches from the North.
Harris arrived in the South Korean capital, Seoul, early on Thursday and the visit comes amid fears that North Korea is about to conduct a nuclear test.
The launch is the latest provocation from Kim Jong-un's authoritarian regime and South Korea, said the launches are an "act of grave provocation."
A White House statement said: "They [Harris and South Korean President Yoon Suk-yeol] condemned the Democratic People's Republic of Korea's provocative nuclear rhetoric and ballistic missile launches.
"They discussed our response to potential future provocations, including through trilateral cooperation with Japan."
North Korean leader Kim Jong Un has said they are developing nuclear weapons and missiles to defend against so-called US threats.
Some say the launches are a chance for him to reassert his authority and grab the attention of the United States.
Experts say the increased number of tests are aimed at the United States, North Korea wants to push them into a corner of accepting the state as a nuclear power.
They hope this would then result in negotiating economic and security concessions for the country which is in a crisis.
Yasukazu Hamad, Minister of Defense of Japan, said following the first launch over the weekend that the "recent remarkable development of nuclear missile-related technologies cannot be overlooked for the security of our country and the region."
His full statement said: "If you include launches of cruise missiles this is the nineteenth launch, which is an unprecedented pace.
"North Korea's action represents a threat to the peace and security of our country, the region and the international community and to do this as the Ukraine invasion unfolds is unforgivable."
