North Korea fired four ballistic missiles almost 1,000 kilometers (620 miles) towards the Sea of Japan early Monday morning, in what Japan's leader described as "an extremely dangerous action."
Military in South Korea, Japan and the United States all confirmed the launch of four projectiles, which one US official said were intermediate range missiles.
Three landed inside Japan's exclusive economic zone, Prime Minister Shinzo Abe said, which extends 200 nautical miles from its coastline according to international maritime law.
Speaking to the Japanese Parliament Monday, Abe said the launch was a clear violation of UN Security Council resolutions.
Experts said the move was almost certainly in reaction to joint military exercises between South Korea and the United States, which Pyongyang views as preparations for an invasion.
The launch took place in Tongchang-ri, in North Korea's North Pyongan province. A spokesperson for South Korea's Joint Chiefs of Staff said the missiles flew as high as 260 kilometers (162 miles).
Acting President Hwang Kyo-ahn told the South Korean National Security Council Monday he strongly condemned North Korea's actions.
"This is a direct challenge to the international community and a grave violation," he said.
"Having seen the brutality of North Korea from Kim Jong Nam, I'd say the consequences of the Kim Jong Un regime having nuclear weapons will be horrible," he said referring to the killing of the North Korean leader's estranged half brother at Kuala Lumpur airport last month. North Korea has denied any involvement in the murder.
The US State Department said it remained "prepared to use the full range of capabilities at our disposal against this growing threat."
"The DPRK's provocations only serve to increase the international community's resolve to counter the DPRK's prohibited weapons of mass destruction programs," acting State Department spokesman Mark Toner said in a statement.
Foal Eagle drills
South Korea and United States' annual military exercises, known as Foal Eagle and which both countries say are defensive in nature, began on Wednesday March 1 and are expected to last until April 30.
North Korea has already denounced this year's exercises through state media service KCNA.
"Now that the US imperialists and the South Korean puppet forces again kicked off the dangerous nuclear war drills against the DPRK at its doorstep, our army will counter them with the toughest counteractions," it said.
The exercises usually draw condemnation and retribution from Pyongyang.
"They (are) making it clear that as long as the US continues these exercises, North Korea will keep taking steps to bolster their deterrent," Jeffrey Lewis, Adjunct Professor at the Middlebury Institute of International Studies told.
During last year's drills, North Korea fired multiple short to medium range missiles and announced it could place nuclear warheads on its weapons.
North Korean missile tests:
This isn't the first time North Korea has launched multiple missiles over this distance.
In September 2016, North Korea launched three ballistic missiles about 1,000 kilometers to land in Japan's Air Defense Identification Zone, provoking a strong response from the country.
Monday's launch comes weeks after North Korea test-fired a new type of missile, the Pukguksong-2, a medium-long range ballistic missile.
Why North Korea's new missile matters:
That missile was also fired from North Pyongan province and traveled 500 kilometers (310 miles) before landing in the Sea of Japan.
The launch happened while Japanese Prime Minister Shinzo Abe was in the United States visiting US President Donald Trump.
North Korean state media reported that Kim Jong Un personally oversaw the operation