The US, UK, France and Germany have imposed fresh sanctions on Iran for supplying Russia with ballistic missiles for use in Ukraine.
The measures include restrictions on national carrier Iran Air's ability to fly to the UK and Europe, and travel bans and asset freezes on a number of Iranians accused of facilitating military support for Russia.
Visiting London, US Secretary of State Antony Blinken said Russians had been trained by Iranian forces to use short-range ballistic missiles and that they could be deployed against Ukrainians within weeks.
Iran has repeatedly denied supplying such self-guided weapons to Russia.
At a joint news conference with UK Foreign Secretary David Lammy on Tuesday, Blinken asserted that Russian President Vladimir Putin was "increasingly relying on support" for Iran and North Korea to help "wage his war of aggression on Ukraine" in violation of multiple UN Security Council resolutions.
He said the US had recently shared intelligence with its partners showing that dozens of military personnel had been trained in Iran to use the Fath-360 ballistic missile system, which has a maximum range of 75 miles (120km).
Lammy said the move was "a significant and dangerous escalation”.
The missiles are likely to boost Russia's arsenal, enabling it to hit Ukrainian cities close to Russia's borders or areas it already controls at the same time as it deploys its longer-range missiles deeper into Ukrainian territory.
The UK Foreign Office said the US and UK sanctions targeted several key individuals heavily involved in the ballistic missile and drone supply chains.
They included Brig Gen Seyed Hamzeh Ghalandari, who it said was director general for international relations at Iran’s defence ministry and was linked to its exports of defence products to its partners.
Sanctions have also been imposed on five Russian cargo ships for transporting the military supplies from Iran, despite what the UK said were repeated warnings not to do so.
Additionally, several organisations, including some allegedly involved in the production of Iran's kamikaze-style Shahed drones - which Russia has used consistently in attacks on Ukrainian cities - have been sanctioned.
In a statement, the UK, France and Germany - known as the E3 - said Iran's supply of missiles represented a "a direct threat to European security".
But Iran called the Western statements "false and misleading".
The Western sanctions come as Russia has continued to make gains in eastern Ukraine, with Moscow's forces rapidly approaching the key settlement of Pokrovsk - an essential transport hub.
UK Prime Minister Sir Keir Starmer has made clear the UK government will continue to back Ukraine for as long as needed.
But Ukrainian President Volodymyr Zelensky has criticised the pace of weapons deliveries, and asked for authorisation to strike targets deep inside Russia with Western-supplied missiles - a move the US has thus far resisted.
Blinken and Lammy also announced a joint trip to Ukraine this week, the first such trip in years as UK diplomats seek to frame the secretary of state's visit as a reaffirmation of a close partnership between the two countries, often described as the "special relationship".
Blinken said one of their goals ahead of the visit was to "hear directly from the Ukrainian leadership" about their "objectives and what we can do to support those needs".
