WASHINGTON — The United States and allies warned Iran on Friday that major Western economies will pile new sanctions on Tehran if it moves forward with an advancing plan to provide ballistic missiles to Russia for its war with Ukraine.

The Biden administration has raised alarms for months that Russia is seeking close-range ballistic missiles from Iran as Moscow struggles to replenish its dwindling supplies.

The U.S. has yet to confirm that missiles have moved from Iran to Russia. But U.S. officials are alarmed by comments by Iranian officials that suggest that a deal is imminent.

Proposed Sanctions

One action that the Group of Seven countries are mulling is to prohibit Iran Air, the country’s national air carrier, from flying to Europe, according to a senior Biden administration official. The official, who was not authorized to comment and insisted on anonymity, declined to preview other sanctions that the U.S. is mulling beyond describing the potential action as “significant measures.”

“Were Iran to proceed with providing ballistic missiles or related technology to Russia, we are prepared to respond swiftly and in a coordinated manner including with new and significant measures against Iran,” the G-7 leaders said in a statement.

Iran’s U.N. Mission said last month that there are no legal restrictions to prevent it from making ballistic missile sales but that is “morally obligated to refrain from weapon transactions during the Russia-Ukraine conflict to prevent fueling the war.”

Existing Sanctions

The U.S. and Europe already impose extensive sanctions against Iran targeting individuals as well as limiting the country’s access to trade, financial services, energy, technology and other sectors. The sanctions on Iran are arguably the most extensive and comprehensive set of sanctions that the United States maintains on any country, with thousands of individuals and entities targeted.

The Democratic administration in January said that U.S. intelligence officials had determined a Russian-Iran deal had not been completed but that they were concerned that Russia’s negotiations to acquire missiles from Iran were actively advancing.

Concerns Over Missile Deal

In September, according to the White House, Iran hosted Russian Defense Minister Sergei Shoigu to show off a range of ballistic missile systems — a moment that sparked U.S. concern that a deal could come together.

The U.S. and other countries have taken steps aimed at thwarting the supply, sale or transfer involving Iran and ballistic missile-related items, including issuing guidance to private companies about Iranian missile procurement practices to make sure they aren’t inadvertently supporting Iran’s development efforts.

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

The Biden administration has repeatedly sought to make the case that the Kremlin has become reliant on Iran and North Korea for the arms it needs to fight its war against Ukraine and has disclosed intelligence findings that it says show as much.

Russia has acquired and used North Korean ballistic missiles against Ukraine. Ukrainian officials, however, say that North Korean missiles when deployed by Russian forces have frequently missed targets.

Russia has received hundreds of one-way attack drones, as well as drone production-related equipment, from Iran, according to the White House. The Biden administration also has accused Tehran of providing Russia with materials to build a drone manufacturing plant east of Moscow.