Prime Minister Shinzo Abe held a phone call with US President Trump but the two leaders 'did not discuss military action'.
Japan says it has agreed with the US on the need for more action against North Korea, hours after Washington issued another warning to Pyongyang and boosted its military activity in the region.
It follows North Korea’s long-range test on Friday, launching a missile that landed in the sea off Japan.
In Tokyo the prime minister spoke to the US president on the phone for nearly an hour, according to officials.
“President Trump and I completely agreed that we must also take further action… We will make every possible effort to protect our citizens’ safety against the threat from North Korea,” Shinzo Abe told reporters.
The prime minister said both leaders thought repeated international efforts to find a solution had not borne fruit – but he did not spell out what steps might be taken.
Officials say the two countries did not discuss military action against North Korea.
The US has responded to Pyongyang’s moves over the weekend by testing an anti-missile system based in Alaska. A missile was fired from a US cargo plane above the Pacific and intercepted.
Washington also flew bombers over the Korean peninsula alongside South Korean and Japanese planes.
The US has called on China to take a stand on stronger UN sanctions against North Korea.