Leaders of the US, UK, and Australia say they share a "mutual interest" in maintaining security in the Indo-Pacific. They have been keeping a close eye on Chinese military activities in the region as part of what they call the AUKUS partnership. Now, they have outlined their approach to deterrence with nuclear submarines.

US President Joe Biden welcomed his counterparts for talks in San Diego, California, on Monday at the home of the US Pacific Fleet.

He said, "Our unprecedented, trilateral cooperation I believe is testament to the strength of the longstanding ties that unite us and to our shared commitment of ensuring the Indo-Pacific remains free and open."

The leaders say they will send US and British submarines to Australia to help train crews there. The US also plans to sell Australia up to five of its latest fast attack Virginia-class submarines. They say that, by sharing technology, the Australians will be able to build their own fleet.

The AUKUS pact was launched in 2021 to counter China's development of hypersonic weapons and other high-tech military capabilities.

Leaders in Canberra say they need to modernize their fleet in light of what they call a worsening "strategic environment." However, that caused them to back out of a major deal with France for diesel-powered subs.

Chinese diplomats have criticized the agreement as a threat to peace in the region. They say it poses a "serious" risk of nuclear proliferation.