Ukrainian President Volodymyr Zelensky returned to the frontline near the devastated city of Bakhmut Wednesday, promising to “respond to every blow” following a string of Russian attacks on civilian sites across Ukraine that killed at least eight people and injured dozens on Wednesday.

In Moscow, Russian officials have warned the United Kingdom not to send ammunition to Ukraine containing depleted uranium. The metal is a byproduct of the enrichment process used to make nuclear warheads and fuel for power plants. It’s both toxic and radioactive and has been linked to congenital birth defects, cancer and kidney damage. This is Russian Foreign Minister Sergey Lavrov speaking Wednesday.

Sergey Lavrov: “While there is no convention to ban depleted uranium shells, the United Nations General Assembly regularly considers resolutions calling on nations not to produce or use depleted uranium. Every time, the United Kingdom, the United States and France vote it down.”

Since the 1990s, the U.S. has fired munitions containing hundreds of tons of depleted uranium in Iraq, Serbia, Kosovo and Syria, as well as the former U.S. Naval Training Range in Vieques, Puerto Rico.