The United States formally accused Iran on Tuesday of supplying short-range ballistic missiles to Russia for its war in Ukraine and will take measures to punish those involved. US Secretary of State Antony Blinken, speaking alongside British Foreign Secretary David Lammy during a visit to London, said that sanctions would be announced later Tuesday.

“Russia has now received shipments of these ballistic missiles and will likely use them within weeks in Ukraine, against Ukrainians,” Blinken said. “The supply of Iranian missiles enables Russia to use more of its arsenal for targets that are further from the front line.”

His comments came as he and Lammy prepare to make a joint visit to Ukraine on Wednesday and as the Kremlin tries to repel Ukraine’s surprise offensive that has claimed hundreds of miles of territory in Russia’s Kursk region.

Ukrainian President Volodymyr Zelenskyy also has ramped up pressure on the US and other allies to allow his country to use Western-supplied missiles to strike deep inside Russia and hit sites from which Moscow launches aerial attacks.

Lammy called the Iranian missile transfers to Russia “a troubling pattern that we’re seeing. It is definitely a significant escalation.”

Iran has denied providing Russia with weapons for its war in Ukraine.

“Iran considers the provision of military assistance to the parties engaged in the conflict — which leads to increased human casualties, destruction of infrastructure, and a distancing from ceasefire negotiations — to be inhumane,” according to a recent statement from Iran’s mission to the United Nations. “Thus, not only does Iran abstain from engaging in such actions itself, but it also calls upon other countries to cease the supply of weapons to the sides involved in the conflict.”

Word of the alleged transfers began to emerge over the weekend with reports that US intelligence indicated they were underway, according to people familiar with the matter who spoke on condition of anonymity

.The US and its allies have been warning Iran for months not to transfer ballistic missiles to Russia.

“Any transfer of Iranian ballistic missiles to Russia would represent a dramatic escalation in Iran’s support for Russia’s war of aggression against Ukraine and lead to the killing of more Ukrainian civilians,” National Security Council spokesman Sean Savett said in a statement Saturday.