Donald Trump has said North Korea is "a threat to the civilised world" and vowed that the US "will not stand" for Pyongyang menacing America or its allies.
The US president, speaking in Tokyo, one of the Asian capitals threatened by North Korea's missiles, did not rule out military action.
He exhorted dictator Kim Jong Un to cease weapons testing such as the missiles he has fired over Japanese territory in recent weeks.
The president also denounced efforts by the Obama administration to manage Pyongyang, declaring again that "the era of strategic patience was over".
He said: "Some people say my rhetoric is very strong but look what has happened with very weak rhetoric in the last 25 years."
Mr Trump, who was with Prime Minister Shinzo Abe of Japan at a news conference, said North Korea endangered "international peace and stability".
Mr Abe has taken a more hawkish view on North Korea than some of his predecessors.
He agreed with Mr Trump's assessment that "all options on the table" when dealing with Kim and announced new sanctions against several dozen North Korea individuals.
The two men also met anguished families of Japanese citizens snatched by Pyongyang's agents, as Mr Trump called their abductions "a tremendous disgrace".
Mr Trump pledged to work to return the missing to their families, intensifying the pressure on North Korea by elevating the heart-wrenching tales of loss to the international stage.
"We've just heard the very sad stories about family members - daughters, wives, brothers uncles, fathers - it's a very, very sad number of stories that we've heard," the president said.
He and first lady Melania Trump stood with nearly two dozen relatives, some of whom held photos of the missing.
North Korea has acknowledged apprehending 13 Japanese in the 1970s and 1980s, but claims they all died or have been released.
But the Japanese government insists many more were taken - and that some may still be alive.
Mr Trump has delivered harsh denunciations of Kim, belittling him as "Little Rocket Man" but suggested that it would be "a tremendous signal" if North Korea returned the captives.