The U.S. government will supply Ukraine’s military with depleted uranium munitions as part of new military aid it announced Wednesday, totaling $1 billion, that it says will give “new momentum” to Ukraine’s counteroffensive to retake territory from control of Russia’s armed forces.

The aid was announced in Kiev by US Secretary of State Anthony Blinken during an unannounced visit.

“The progress of the developing counter-offensive has been accelerating in recent weeks and this new aid will help it gain new momentum,” he assured during a press conference, flanked by his Ukrainian counterpart Dmytro Kuleba.

In addition to anti-tank missiles, it will also include $300 million for security in recaptured areas, $206 million for humanitarian aid, $200 million for supporting local institutions, $90 million for demining and explosives disposal, and 100 million dollars to finance future purchases of military equipment.

The strictly military component, worth $175 million, provides for the delivery of 120mm depleted uranium shells for the US Abrams main battle tanks, which Kiev is expected to receive in the fall, the Pentagon said in a statement.

The US will also send anti-missile defense systems, and other munitions for HIMARS multiple launch systems, as well as communications equipment.

It is the first time the US has announced it will supply Ukraine with depleted uranium munitions, capable of penetrating tank armor but controversial because of the toxic risks to military and civilians.

Britain already sent such munitions to Kiev earlier this year.

Uranium, an extremely dense metal, does not deform on contact with the target and is therefore used for armor-piercing shells and bombs capable of penetrating thick armor. Ammunition of this kind is available to various armies, including the Russian one. Legally, their use is not prohibited under international law.

When London announced that it would send such munitions to Kiev, Moscow reacted strongly, threatening to use them accordingly.

About two months ago, Washington broke yet another taboo by supplying cluster munitions to the Ukrainian military, a decision that outraged NGOs.

Since the start of the Russia-Ukraine war in February 2022, the US government has sent or pledged more than $43 billion in military aid.

The Russian embassy in the US capital denounced the announcement that depleted uranium munitions would be sent, calling it “inhumanity” and arguing that “the US is deceiving itself by refusing to accept the failure of the so-called counterattack by the Ukrainian military.”