The U.S. Defense Department called North Korea's missile launch a "very serious threat" and said it is taking steps to increase defenses against the communist nation's ballistic missiles.
North Korea fired four ballistic missiles Monday, three of which flew about 1,000 kilometers and landed in Japanese waters.
A Pentagon spokesman, Navy Captain Jeff Davis, told reporters the weapons were medium-range ballistic missiles and did not pose a threat to North America.
An expected response
Davis said the launches coincided with the start of annual defense exercises between the United States and South Korea and "are consistent with North Korea's long history of provocative behavior often timed to military exercises that we do with our ally."
He said the United States is taking steps to increase its ability to defend against the missile launches, including plans for the deployment of the THAAD anti-ballistic missile defense in South Korea. He said that will happen "as soon as feasible."
Davis left open the possibility that more than four missiles were fired by North Korea.
"There were four that landed. There may be a higher number of launches that we're not commenting on," he said.
U.S. President Donald Trump told Japanese Prime Minister Shinzo Abe during a telephone discussion that the United States was with Japan "100 percent," Abe told reporters on Tuesday.
U.S. Defense Secretary Jim Mattis and Japanese Defense Minister Tomomi Inada also spoke on the phone Monday, the Pentagon said, adding both leaders agreed the launches were "unacceptable and irresponsible."
At the United Nations, diplomats said the U.N. Security Council will hold an emergency meeting Wednesday to discuss North Korea's actions.
North Korea's U.N. Ambassador Ja Song Nam urged the U.N. Security Council in a letter to discuss the U.S.-South Korean military exercises, calling them "the most undisguised nuclear war maneuvers." He said the United States is using nuclear-powered aircraft carries, stealth fighters and submarines, and said of the military drills, "it may go over to an actual war."
Missile launches condemned
Countries around the world are condemning the missile launches.
Russian spokesman Dmitry Peskov said "Definitely, we are seriously worried — these are the sort of actions that lead to a rise in tension in the region and, of course, in this situation, traditionally, Moscow calls for restraint from all sides."
China said it opposed the launches and called for restraint from all sides, but also noted that the United States and South Korea are carrying out military drills which it said were against North Korea.
A French foreign ministry statement condemned the missile firings, while British foreign minister Boris Johnson said they were a threat to international peace and security.
'New level of threat'
Abe said that Monday's missiles, which landed only 300-350 km (185-220 miles) from Japan's Oga Peninsula in the Akita prefecture, demonstrated an increased danger to the country. "This launch has clearly indicated that North Korea poses a new level of threat," he said.
South Korea's Acting President Hwang Kyo-ahn also denounced the missile tests after meeting with his National Security Council.
"Our government strongly condemns that North Korea fired ballistic missiles, once again ignoring continuous warnings from South Korea and the international community, as it is a challenge against the international community and a grave act of provocation," he said.
The United Nations condemned the North's missile firings, saying it should refrain from such actions. "We deplore the continued violation of Security Council resolutions by the Democratic People's Republic of Korea, including the most recent launches of ballistic missiles," U.N. spokesman Farhan Haq said.
The head of the United Nation's International Atomic Energy Agency, Yukiya Amano, called on North Korea to fully comply with its obligations under Security Council resolutions. "It is deeply regrettable that the DPRK [Democratic People's Republic of Korea] has shown no indication that it is willing to comply with U.N. Security Council resolutions adopted in response to its two nuclear tests last year," he said.
In the last year, North Korea has accelerated its nuclear and ballistic weapons testing with more than 25 missile launches and two nuclear tests.
The missiles on Monday were launched from the Tongchang-ri region near the North's border with China, said the South Korean military. From this same region at its Tongchang-ri satellite facility, Pyongyang in February of 2016 launched a satellite into space using banned intercontinental ballistic missile technology.
ICBM is not launched
U.S. military leaders have said in the past they believe North Korea has the ability to miniaturize a nuclear warhead to fit on a KN-08 long-range missile, although Pyongyang has not yet demonstrated this capability.
Monday's launch did not include a long-range intercontinental ballistic missile (ICBM) which could potentially travel far enough to target the U.S. mainland.
In January, North Korean leader Kim Jong Un indicated his country would soon test an ICBM. Prior to taking office, U.S. President Donald Trump tweeted a response to Kim saying "it will not happen," implying that Washington would deter Pyongyang from developing the long-range ballistic missile capability.
Carla Babb at the Pentagon contributed to this report.