Russia on Thursday called the US decision to send to Ukraine armor-piercing shells containing depleted uranium for US-made Abrams tanks "a criminal act".

"This is not just an escalatory step, but it is a reflection of Washington's outrageous disregard for the environmental consequences of using this kind of ammunition in a combat zone. This is, in fact, a criminal act, I cannot give any other assessment," Russian Deputy Foreign Minister Sergei Ryabkov said, according to state news agency Tass.

After the Pentagon announced Wednesday that for the first time the US will send the armor-piercing ammunition containing depleted uranium, the Russian embassy in Washington denounced the decision as "an indicator of inhumanity".

"The US is deliberately transferring weapons with indiscriminate effects," the embassy said. "It is fully aware of the consequences: explosions of such munitions result in the formation of a moving radioactive cloud. Small particles of uranium settle in the respiratory tract, lungs, esophagus, accumulate in kidneys and liver, cause cancer and lead to the inhibition of the whole organism's functions."

US officials say the munitions are common and don't present a radioactive threat. The use of depleted uranium shells isn't banned under international law. But their use has been fiercely debated, with opponents such as the International Coalition to Ban Uranium Weapons saying there are dangerous health risks from ingesting or inhaling depleted uranium dust, including cancers and birth defects.

The United Nations Environment Program said in a report last year that the metal's chemical toxicity presents the greatest potential danger, and "it can cause skin irritation, kidney failure and increase the risks of cancer".

US National Security Council spokesman John Kirby said Wednesday that the ammunition isn't radioactive and "not anywhere close to going into" the sphere of nuclear weaponry.

"This is a commonplace type of munition that is used particularly for its armor-piercing capabilities," he said

The Pentagon announcement said that an unspecified number of depleted-uranium tank rounds are part of a new military aid package for Ukraine worth up to $175 million. It is part of more than $1 billion in civilian and defense support that US Secretary of State Antony Blinken announced in the Ukrainian capital, Kyiv, on Wednesday.

The 120 mm rounds will be used to arm the 31 M1A1 Abrams tanks that the US plans to deliver to Ukraine this fall. The armor-piercing rounds were developed by the US during the Cold War to destroy Soviet tanks, including the T-72 tanks that Ukraine now faces in its counteroffensive.

Russia also reacted angrily when the UK announced in March it was sending depleted uranium shells to Ukraine for its Challenger 2 tanks.

When Russian President Vladimir Putin described the weapons as having a "nuclear component", the UK Ministry of Defense said it had used depleted uranium in its armor-piercing shells for decades and accused Moscow of deliberately spreading misinformation.

The move to send the depleted-uranium weapons comes following the White House's decision to send Ukraine cluster munitions, which are banned by more than 100 countries because of their devastating effects, sometimes years later, on children and other civilians who mistakenly disturb and detonate unexploded rounds.

The New York Times reported Thursday that three American officials, who were not named, said that the Biden administration is planning to send more cluster munitions and soon because they were key to helping Ukrainian troops gain momentum.

In March, the Pentagon said it wouldn't be sending any depleted uranium munitions to Ukraine. But last week Reuters reported that the US had decided to send the munitions. A Department of Defense

official told the Politico website that the US decided to send the weapons because they were thought to be the best way of arming Abrams tanks in Ukraine.

The reversal comes after months of debate over the armor-piercing rounds at the White House, where some officials expressed concern that sending the rounds might open Washington to criticism that it was providing a weapon that may carry health and environmental risks, The Wall Street Journal reported in January.

US officials cite studies by the International Atomic Energy Agency (IAEA), the United Nations' nuclear watchdog, showing "the existence of depleted uranium residues dispersed in the environment does not pose a radiological hazard to the population of the affected regions".