HIROSHIMA, Japan — Leaders of the world’s most powerful democracies warned China and North Korea against building up their nuclear arsenals, pivoting to major northeast Asian crises ahead of the arrival later Saturday of Ukrainian President Volodymyr Zelenskyy.

The focus on Asia at the Group of Seven summit comes as leaders tighten sanctions meant to punish Moscow and change the course of its 15-month invasion of Ukraine. Japan confirmed that Zelenskyy’s decision to attend the G7 in person stemmed from his “strong wish” to participate in talks that will influence his nation’s defense against Russia.

U.S. National Security Adviser Jake Sullivan said that President Joe Biden and Zelenskyy would have direct engagement at the summit, a day after Biden announced his support for training Ukrainian pilots on U.S.-made F-16 fighter jets, a precursor to eventually providing those aircraft to Ukraine’s Air Force.

World leaders have faced a high-stakes balancing act in Hiroshima as they look to address a raft of global worries demanding urgent attention, including climate change, AI, poverty and economic instability, nuclear proliferation and, above all, the war in Ukraine.

China, the world’s No. 2 economy, sits at the nexus of many of those concerns.

There is increasing anxiety in Asia that Beijing, which has been steadily building up its nuclear bomb program, could try to seize Taiwan by force, sparking a wider conflict. China claims the self-governing island as its own and regularly sends ships and warplanes near it.

The G7 leaders issued a statement warning that China’s “accelerating build-up of its nuclear arsenal without transparency (or) meaningful dialogue poses a concern to global and regional stability.”

North Korea, which has been testing missiles at a torrid pace in an attempt to perfect a nuclear program meant to target the mainland United States, must completely abandon its nuclear bomb ambitions, the leaders said, “including any further nuclear tests or launches that use ballistic missile technology. North Korea cannot and will never have the status of a nuclear-weapon State under” international nuclear treaties, the statement said.

The green light on F-16 training is the latest shift by the Biden administration as it moves to arm Ukraine with more advanced and lethal weaponry, following earlier decisions to send rocket launcher systems and Abrams tanks. The United States has insisted that it is sending weapons to Ukraine to defend itself and has discouraged attacks by Ukraine into Russian territory.

“We’ve reached a moment where it is time to look down the road again to say what is Ukraine going to need as part of a future force, to be able to deter and defend against Russian aggression as we go forward,” Sullivan said.

An EU official, speaking on condition of anonymity to brief reporters on the deliberations, said Zelenskyy will take part in two separate sessions Sunday. The first session will be with G7 members only and will focus on the war in Ukraine.