Donald Trump has said "all options are on the table" for a US response to North Korea's launch of a missile over Japan.
In a written statement, the US president said North Korea has "signalled its contempt for its neighbours, for all members of the United Nations, and for minimum standards of acceptable international behaviour".
"Threatening and destabilising actions only increase the North Korean regime's isolation in the region and among all nations of the world," Mr Trump added. "All options are on the table."
In a first, North Korea on Tuesday fired a mid-range ballistic missile designed to carry a nuclear payload that flew over Japan and splashed into the northern Pacific Ocean, officials said.
The launch over the territory of a close US ally sent a clear message of defiance as Washington and South Korea conduct war games nearby.
Mr Trump's statement implies that military action remains an option in resolving the stand-off over North Korea's development of nuclear weapons that could threaten America.
The US administration has in recent weeks been emphasising it wants to use economic and diplomatic pressure to achieve a negotiated solution.
Mr Trump and Japanese prime minister Shinzo Abe conferred by telephone over the latest missile test.
The White House said the leaders agreed that North Korea poses "a grave and growing direct threat" to the United States, Japan, South Korea and countries around the world.
"President Trump and prime minister Abe committed to increasing pressure on North Korea, and doing their utmost to convince the international community to do the same," the White House said.
Mr Abe said in a statement that "Japan's and the US positions are totally at one".
The prime minister added that both nations were in "total agreement" that an emergency meeting was needed at the UN Security Council to step up pressure on North Korea after what he called an unprecedented threat.
He also said Mr Trump expressed his "strong commitment" to defending Japan.
North Korea's latest test came weeks after the UN Security Council voted unanimously to impose tough new sanctions against the government in Pyongyang.
It also followed a series of missile launches late on Friday, and came after a period in which the US and North Korea had traded heated rhetoric over Pyongyang's continued missile tests, which violate UN Security Council resolutions.
Mr Trump last week praised North Korea's decision to back down from its earlier threats to attack the US territory of Guan.
"I respect the fact that I believe he (Kim Jong Un) is starting to respect us," Mr Trump said at a campaign rally in Phoenix. "I respect that fact very much. Respect that fact. And maybe, probably not, but maybe something positive can come about."