The United States on Thursday announced a new $150 million military assistance package for Ukraine that includes artillery and small-arms ammunition as well as anti-tank weapons.

Washington is by far Kyiv's biggest donor of security aid, committing $43.9 billion since Russian forces invaded in February 2022.

But opposition from hardline Republican lawmakers has put future assistance for Kyiv in doubt, and the US government is now relying on previously approved aid in the absence of new funding from Congress.

The latest package "utilizes assistance previously authorized for Ukraine during prior fiscal years," the Pentagon said in a statement.

"The Biden administration calls on Congress to meet its commitment to the people of Ukraine by passing additional funding to ensure Ukraine continues to have what it needs to defend itself against Russia's brutal war of choice," the statement said.

The package also includes air defense missiles, night vision devices, demolition munitions, and cold weather gear.

US officials have spearheaded the push for international support for Ukraine, quickly forging a coalition to back Kyiv after Russia invaded and coordinating aid from dozens of countries.