WASHINGTON (AP) — The White House on Monday said Russia is looking to buy additional advanced attack drones from Iran for use in its war against Ukraine after using up most of the 400 drones it had previously purchased from Tehran.

The Biden administration last year publicized satellite imagery and intelligence findings that it said indicated Iran sold hundreds of attack drones to Russia. And for months, officials have said the United States believed Iran was considering selling hundreds of ballistic missiles to Russia, but Washington did not have evidence a deal was consummated.

“Iran also continues to provide Russia with one-way attack UAVs (unmanned aerial vehicles). Since August, Iran has provided Russia with more than 400 UAVs primarily of the Shahed variety,” White House National Security Council spokesman John Kirby said.

“Russia has expended most of these UAVs, using them to target Ukrainian critical infrastructure inside Ukraine. By providing Russia with these UAVs, Iran has been directly enabling Russia’s war of aggression in Ukraine,” Kirby told reporters.

The Shahed drones that Russia has already purchased are packed with explosives and programed to loiter overhead until they nosedive into a target — unmanned versions of World War II kamikaze pilots who would fly their explosives-laden planes into U.S. warships in the Pacific.

Kirby said the Russians are now looking at acquiring even more advanced drones “capable of more lethality”

The latest revelation is part of a persistent drip of intelligence findings from the administration to detail what U.S. officials say is a deepening defense partnership between Russia and Iran. The U.S. allegations are part of a broader effort to declassify and publicize intelligence findings concerning Moscow’s prosecution of its nearly 15-month war in Ukraine in hopes of furthering global isolation of Russia.

Meanwhile, British Prime Minister Rishi Sunak’s office announced Monday it was sending Ukraine hundreds more air defense missiles, as well as “long-range attack drones” with a reach of more than 200 kilometers (120 miles). The announcement came as Ukrainian President Volodymyr Zelenskyy visited Britain and unsuccessfully pressed Sunak to provide Ukraine with fighter jets as Ukraine prepares for a long-anticipated spring offensive to retake territory that Russia has seized.

The Biden administration says the Kremlin’s reliance on Iran as well as North Korea— countries largely isolated on the international stage for their nuclear programs and human rights records— shows desperation. That’s in the face of Ukrainian resistance and the success of the global coalition in disrupting Russian military supply chains and denying replacements for weapons lost on the battlefield. The White House says Russia has turned to North Korea for artillery.

U.S. officials say Iran has also provided Russia with artillery and tank rounds for its invasion of Ukraine.

“This is a full scale defense partnership that is harmful to Ukraine, to the region in the Middle East and to the international community,” said Kirby, who added that Iran has been “Russia’s top military backer” since the start of the Ukraine invasion.

Kirby said the administration is looking to further tighten export controls to prevent Western components from making their way to Iran for use in manufacturing drones. He also said further sanctions against Iran and Russia could be coming.

Iran has said it provided drones to Russia prior to the start of the war, but not since. North Korea has denied it has provided Russia artillery.

The White House has said for months that it has seen troubling signs that the military cooperation between Moscow and Tehran could flow both ways.

Iran is seeking to purchase additional military equipment from Russia, including attack helicopters, radars, and YAK-130 combat trainer aircraft, according to the White House. And Iran last month announced that it had finalized a deal to buy Su-35 fighter jets from Russia.

The White House has also previously said Russia and Iran were considering starting a drone assembly line in Russia for the Ukraine conflict.

“In total, Iran is seeking billions of dollars’ worth of military equipment from Russia,” Kirby said.

The new allegations come as Biden is headed to Hiroshima, Japan, later this week for the Group of Seven summit, where the U.S. president is expected to make a call to fellow leaders of some world’s biggest economies to further tighten export controls and sanctions on Moscow.

This article first appeared on APnews.com