The 120mm rounds are for the US M1 Abrams tanks that Washington has promised to Kyiv and which are expected to be delivered before the end of the year.

Depleted uranium munitions are controversial due to their association with health problems such as cancer and birth defects in areas where they were used in past conflicts, though they have not been definitively proven to have caused such issues.

The density of depleted uranium -- a by-product of the nuclear enrichment process -- helps rounds that contain it punch through heavy armor, making it ideal for use in ammunition designed to target tanks.

Depleted uranium munitions are part of the military arsenals of many countries, including those of the United States and Russia, and its use is not banned under international law.

Britain said earlier this year that it would provide Kyiv with armor-piercing ammunition containing depleted uranium, after which Russian President Vladimir Putin threatened to begin using it in Ukraine.

The US promise of depleted uranium rounds comes about two months after Washington said it would provide cluster munitions to Ukraine -- a controversial decision that drew sharp criticism from rights groups due to the danger unexploded bomblets pose.

- Anti-tank missiles, artillery ammo -

The latest US assistance package for Ukraine also includes anti-tank missiles, artillery and mortar rounds, small arms ammunition, and demolitions munitions for clearing obstacles, the Pentagon said in a statement.

The aid -- which comes as Ukraine battles Russian forces in a slow-moving counteroffensive -- will be drawn from existing US military stocks.

Ukraine launched its counteroffensive against Russian troops in June after building up Western-supplied weapons, and has repeatedly hit back at criticism for its apparent slow pace and limited gains.

Top US diplomat Antony Blinken said during a visit to Kyiv on Wednesday that Washington would "maximize" efforts to support Ukraine, which he described as making "important progress" in its counteroffensive.

Ukrainian Foreign Minister Dmytro Kuleba told Blinken that Washington's support was "not charity," saying: "Today, thanks to our partners, Ukraine is restraining Russia's aggression."

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

Washington has promised Kyiv more than $43 billion in military assistance since Moscow launched its full-scale invasion in February 2022.

Ukraine's supporters have also provided training to Kyiv's troops, while the United States and other countries have imposed tough sanctions on Russia, with targets including financial institutions, technology imports and energy exports.