The White House said Tuesday the United States, United Kingdom and Australia agreed to cooperate on developing hypersonic weapons and other defensive capabilities under the AUKUS security pact.

Why it matters: The new announcements deepen the collective defense agreement between the countries as means to counter China in the Indo-Pacific region, though the leaders said they reiterated their commitment to the pact Tuesday in part because of Russia's invasion of Ukraine.

• The trilateral security partnership was announced in September as an effort to help Australia acquire nuclear-powered submarines and develop advanced defense technologies, primarily as a warning to China.
• The U.S. announced earlier Tuesday that it recently completed its second in-flight test of a hypersonic cruise missile.

What they're saying: The White House said in a statement released after a meeting between Australian Prime Minister Scott Morrison, U.K. Prime Minister Boris Johnson and President Biden that the leaders reaffirmed their commitment to AUKUS and "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," the statement reads.
• The leaders said they will also coordinate on counter-hypersonic systems and electronic warfare, while expanding information sharing and defense innovation between the countries.

The big picture: China's hypersonic missile test last year caught U.S. intelligence officials by surprise, while Biden recently confirmed that Russian forces have used hypersonic missiles against Ukrainian targets.

• Hypersonic missiles are highly maneuverable in flight, making them difficult to detect on radars and destroyed with missile defense systems.

Go deeper: U.S. completes second hypersonic missile flight test