Japan's Prime Minister Kishida Fumio has met separately with other G7 leaders before the group's summit gets underway.
Kishida met US President Joe Biden at a hotel in Hiroshima on Friday.
At the start of the meeting, Kishida said, "At the summit, I want to show the G7 nations' unwavering commitment to safeguarding a free and open international order based on the rule of law, which Japan and the United States have been upholding."
Biden replied, "We stand up for the shared values including supporting the brave people of Ukraine as they defend their sovereign territory and holding Russia accountable for its brutal aggression. And we're tracking the global challenges, from strengthening our community and our commitment to nuclear nonproliferation to ensuring a free and open Indo-Pacific that's at the heart of all this."
The bilateral talks come as the countries are boosting the deterrence and response capabilities of their alliance amid growing concerns over China and North Korea.
Japan and the US are also working together to strengthen supply chains of semiconductors and key minerals.
At the G7 summit, Kishida hopes to highlight the risks of nuclear weapons in a city that was the site of the world's first atomic bombing in 1945.
He says he wants to reaffirm the G7's determination toward a world without nuclear weapons.
Food security and the state of the global economy will also be on the agenda.