The United States and its allies warned Iran’s regime on Friday that major Western economies would impose significant new sanctions if Tehran proceeds with a plan to supply ballistic missiles to Russia for its war in Ukraine.

U.S. intelligence has long been concerned about a potential deal between Iran and Russia. In January, officials reported negotiations were actively progressing, and in September, Iran’s regime reportedly showcased ballistic missile systems to visiting Russian Defense Minister Sergei Shoigu.

While the Iranian regime claims no legal restrictions prevent the sale, it has also expressed a moral objection to fueling the conflict. However, the constant reports from the Ukrainian government of shooting down Iranian regime drones used by Russia against Ukrainian cities and its people point to something else.

The U.S. and Europe already have extensive sanctions on Iran, restricting trade, finance, energy, and technology. These sanctions could be significantly tightened if Iran delivers the missiles.

“We’ve sent very clear messages to Iran not to do it,” Secretary of State Antony Blinken said during a news conference on Friday. “This is a subject of considerable conversation among a number of countries.”

The Biden administration is particularly concerned about Russia’s growing reliance on the Iranian regime for weapons. While Russia has already used North Korean ballistic missiles with limited success, it has also received hundreds of drones and drone production equipment from Iran. The U.S. even accuses Tehran of providing materials for a drone manufacturing plant near Moscow.

Iran’s regime initially denied supplying drones, but later acknowledged a small number before the invasion. The potential missile sale raises the stakes considerably, prompting the strong warnings from the West.