The US has warned it is ready to use force if needed to stop North Korea's nuclear missile program, but says it prefers global diplomatic action.
It comes after Pyongyang defied world powers by test launching a ballistic missile that could hit Alaska.
US Ambassador to the United Nations Nikki Haley told a meeting of the UN Security Council that North Korea's actions were "quickly closing off the possibility of a diplomatic solution" and the US is prepared to defend itself and its allies.
"One of our capabilities lies with our considerable military forces. We will use them if we must, but we prefer not to have to go in that direction," Haley said. She urged China, North Korea's only major ally, to do more to rein in Pyongyang.
Speaking with his Japanese counterpart on Wednesday, US Defense Secretary James Mattis underscored the "ironclad commitment" of the US to defending Japan and providing "extended deterrence using the full range of US capabilities," Pentagon spokeswoman Dana White said in a statement.
Taking a major step in its missile program, North Korea on Tuesday test launched an intercontinental ballistic missile that some experts believe has the range to reach the US states of Alaska and Hawaii and perhaps the US Pacific Northwest.
North Korea says the missile could carry a large nuclear warhead.
The missile test is a direct challenge to US President Donald Trump, who has frequently urged China to press the isolated country's leadership to give up its nuclear program.
Haley said the United States would propose new UN sanctions on North Korea in coming days and warned that if Russia and China did not support the move, then "we will go our own path."
China's UN ambassador, Liu Jieyi, told the Security Council meeting that the missile launch was a "flagrant violation" of UN resolutions and "unacceptable."
North Korean leader Kim Jong Un said the ICBM test completed his country's strategic weapons capability that includes atomic and hydrogen bombs, the state KCNA news agency said.
"He, with a broad smile on his face, told officials, scientists and technicians that the US would be displeased ... as it was given a 'package of gifts' on its 'Independence Day,'" KCNA said, referring to the missile launch on July 4.
Trump and other leaders from the Group of 20 nations meeting in Germany this week are due to discuss steps to rein in North Korea's weapons program, which it has pursued in defiance of Security Council sanctions.
Russia's deputy UN envoy said on Wednesday that military force should not be considered against North Korea and called for a halt to the deployment of a US missile defense system in South Korea.
He also said that attempts to strangle North Korea economically were "unacceptable" and that sanctions would not resolve the issue.