WASHINGTON — US President Joe Biden and Japan's prime minister have vowed to strengthen defense cooperation in the face of a potential threat from China.

The plans announced by Biden and Fumio Kishida during his Washington visit include an expanded air defense network incorporating Australia.

Additionally, Biden said a Japanese astronaut would join Nasa's Artemis program to put people on the Moon.

The astronaut will become the first non-American on the Moon's surface.

Speaking from the Rose Garden of the White House during Kishida's state visit to Washington, Biden said that the deals constituted "the most significant upgrade of our alliance since it was first established".

Over the course of about two hours of talks, the two leaders largely focused on defence matters in the Indo-Pacific, as well as the ongoing conflicts in Ukraine and Gaza.

North Korea, Taiwan and China were a particular focus of the discussions, Kishida said, calling on an "international order based on the rule of law" to be maintained.

"Unilateral attempts to change the status quo by force or coercion is absolutely unacceptable, wherever it may be," Kishida said.

"Regarding Russia's aggression of Ukraine...Ukraine today may be East Asia tomorrow," he added.

As part of the agreements, Biden said that the US military would establish a joint command structure with its Japanese counterparts.

The two allies will also develop a joint air and missile defense network in the region along with Australia, as well as participate in three-way military exercises, along with UK forces.

Kishida acknowledged that, while the US and Japan would continue to respond to "challenges" from China, they "confirmed the importance of continuing our dialogue with China and co-operating with China on common challenges".

In the space sector, Japan will provide and operate a "pressurised lunar rover", while the US will allow two Japanese astronauts to take part in Nasa's Artemis missions and — eventually — allow a Japanese astronaut to become the first non-American to land on the Moon.

At a welcome ceremony earlier in the day, Biden said the US and Japan had become "the closest of friends".

The two leaders also briefly addressed the recent move by Japan's Nippon Steel to purchase US Steel for about $15bn (£11.9bn), with Kishida saying that Japan hopes the deal "will unfold in directions that would be positive for both sides".

Biden, for his part, vowed to "stand by" American workers as well as the US-Japan alliance. In an unusual move last month, the US president said the "iconic" US firm should remain in American hands.

Japan is the largest foreign investor into the US, with more than one million Americans employed by Japanese companies.

"Investment from Japan to the US can only increase upwards in the months and years to come," Kishida said. "And we wish to cement this win-win relationship."

The visit continued on Wednesday night with a lavish state dinner.

In a formal toast at the event, both Biden and Kishida toasted the US-Japan relationship, with Kishida quoting former President John F Kennedy's remark that the Pacific Ocean "unites" the two countries.

"We are now standing at the turning point in history, embarking on a new frontier," Kishida said, before referencing Star Trek and telling guests "boldly go" where nobody has gone before.

The event — which the White House said is themed on "the bounty of spring" — will include a musical performance by US musician Paul Simon.

In addition to lawmakers and officials from both countries, the dinner's guest list includes actor Robert De Niro, Apple CEO Tim Cook, Bill and Hillary Clinton, former figure skater Kristi Yamaguchi and Amazon founder Jeff Bezos.

On Thursday, Kishida will head to Capitol Hill to address Congress and will participate in a three-way meeting with Biden and Philippines President Ferdinand Marcos Jr that is expected to focus on China. — BBC