US intelligence officials say Iran and Russia continue to strengthen their military cooperation and weapons assistance.

In a statement on Friday, White House National Security Council spokesman John Kirby cited US intelligence findings that indicated Iran had provided material support for the plant, which could be operational by early next year.

US officials also double-downed on claims that Iran has sent hundreds of drones — or unmanned aerial vehicles (UAVs) — to Russia for use in Ukraine, where a full-scale invasion was launched in 2022.

“Russia has been using Iranian UAVs in recent weeks to strike Kyiv and terrorize the Ukrainian population, and the Russia-Iran military partnership appears to be deepening,” Kirby said in Friday’s statement.

“We are also concerned that Russia is working with Iran to produce Iranian UAVs from inside Russia.”

The administration of US President Joe Biden, Ukraine’s most important supporter, had previously alleged that Iran and Russia were discussing the possibility of setting up a drone assembly line inside of Russia.

Kirby said that US intelligence officials now believe that the manufacturing plant is being set up in the Alabuga special economic zone, several hundred miles east of Moscow.

Russia and Iran have indeed strengthened their partnership in recent years, stepping up weapons sales and exploring ways to outmanoeuvre US-led efforts to economically isolate the two countries.

But Russia has denied using Iranian-made drones in Ukraine. Iran, meanwhile, has acknowledged sending drones to Russia but says it did so before Russia’s widely condemned invasion in February 2022.

Nevertheless, the US has accused Iran of complicity in the Russian invasion, which has killed thousands of people and displaced nearly 14 million people, according to the United Nations.

On Friday, Kirby said that Iran has continued to send drones to Russia, shipping them across the Caspian Sea to the Russian port of Makhachkala. The Biden administration has previously sanctioned Iranian defence firms involved in drone production.

“Iran’s well-documented proliferation of UAVs and conventional weapons to its proxies continues to undermine both regional security and global stability,” the US Treasury said in a March statement announcing further sanctions.

Last month, Ukraine approved a package of sanctions against Iran due to its close partnership with Russia. Ukraine has also alleged that Iranian-made drones have been used in Russian attacks on Ukrainian cities that have killed and maimed civilians.

Ukrainian President Volodymyr Zelenskyy asked Iranians if they wanted to be “accomplices in Russian terror”, a statement Tehran dismissed as “political show”.

But Russia has also accused Ukraine of likewise using drones to launch attacks inside its borders. Earlier this week, Russia reported that a drone that crashed into a residential building in the city of Voronezh, and it also blamed Ukraine for a series of drone attacks in Moscow in late May.