The UK, US, and Australia will begin co-operating on research into hypersonic weapons and defences against them, the three countries have said.
The research will be part of the AUKUS military partnership, a security pact announced by the three countries last year, the statement from Boris Johnson, Joe Biden and Australia’s Scott Morrison announced.
Hypersonic weapons can travel at five times the speed of sound, and because of their speed, flight at low altitudes, and ability to manoeuvre, they are harder to defend against.
The Russian military has boasted about its use of hypersonic missiles in Ukraine, the first time it had been used in combat.
In a joint statement, the countries’ leaders said: "We reaffirmed our commitment to Aukus and to a free and open Indo-Pacific.
“In light of Russia’s unprovoked, unjustified, and unlawful invasion of Ukraine, we reiterated our unwavering commitment to an international system that respects human rights, the rule of law, and the peaceful resolution of disputes free from coercion."
“We also committed today to commence new trilateral cooperation on hypersonics and counter-hypersonics, and electronic warfare capabilities, as well as to expand information sharing and to deepen co-operation on defence innovation.
“These initiatives will add to our existing efforts to deepen co-operation on cyber capabilities, artificial intelligence, quantum technologies, and additional undersea capabilities.
“As our work progresses on these, and other critical defence and security capabilities, we will seek opportunities to engage allies and close partners."
The leaders also said they were "pleased with the progress" Australia was making in the development of nuclear-powered submarines.
The initial announcement of the Aukus pact caused outrage in Paris, as the submarine deal came at the expense of a lucrative agreement between Australia and France to provide diesel-electric boats.