Russia and Iran are strengthening their defense partnership, the Biden administration warns.

The Biden administration said on Friday that Russia and Iran were strengthening their military ties into a “full-fledged defense partnership,” warning that their relationship posed a threat to Ukraine as well as Iran’s geographic neighbors.

“Russia is seeking to collaborate with Iran on areas like weapons development and trade,” said John Kirby, a National Security Council spokesman. “As part of this collaboration, we are concerned that Russia intends to provide Iran with advanced military components.”

The Biden administration is aware of reports that the two countries are seeking to establish a joint production line for drones in Russia, Mr. Kirby said, adding that Iranian support for Russia’s military is expected to grow in the coming months.

British officials affirmed the Biden administration’s statements on Friday. “Iran is now one of Russia’s top military backers,” said Britain’s foreign secretary, James Cleverly, calling the “sordid deals” a threat to global security.

Barbara Woodward, the U.K. ambassador to the United Nations, called for an investigation, saying that Iran had violated international law in supplying hundreds of drones to Russia and that Russia was now seeking hundreds of ballistic weapons.

“In return, Russia is offering Iran an unprecedented level of military and technical support,” she said.

Iranian-made drones have been used to attack both military and civilian targets in Ukraine, helping Russia supplement what Ukrainian and Western officials say is a dwindling weapons supply.

The Kremlin has denied using Iranian-made drones to attack civilians, and the Iranian government denied for weeks that it had sent the drones. Amid growing international calls for accountability and new sanctions from the West, Iran acknowledged their delivery in early November, though the Iranian foreign minister maintained that the deliveries had all taken place before Russia invaded Ukraine in February.