Russia's links with Iran are growing stronger - and Ukraine and the West will have to retaliate
The head of the CIA has warned that any move by Iran to supply Russia with ballistic missiles for its war in Ukraine would be a "dramatic escalation" - but Ukrainian sources say this has already happened.
It is part of a pattern of ever-tighter cooperation between Moscow and Tehran, which has already seen the Iranian regime transfer huge quantities of killer drones, ammunition and artillery shells in return for cash and help from Russia on improving its own military technology and manufacturing capabilities.
This includes the alleged gifting by the Kremlin to Iran of captured Western weapons, such as the N-LAW anti-tank missile.
"It is a two-way street," Bill Burns, the CIA director, said in his first public appearance with his British counterpart, Sir Richard Moore, at an event in London at the weekend.
"Russia is able to do a number of things to help Iran's ballistic missiles - to make them more dangerous to use against our friends and partners across the Middle East."
Western officials have long been warning about the potential for Iran to start supplying ballistic missiles to Russia.
Grant Shapps, when he was defence secretary, signalled in an interview with House Magazine in March, that a transfer had already happened after the Reuters news agency reported that around 400 such munitions had been transferred.
Then on Saturday, multiple news organisations - including Sky News, citing a Ukrainian source - reported that Iran had supplied Russia with more than 200 short-range, Fatah-360 ballistic missiles.
Iran has yet to comment and has in the past denied the allegations.
The regime had previously held off from offering up its vast stockpiles of precision-guided missiles, amid the threat of further Western sanctions and international isolation.
However, its calculations appear to have changed following the expiry last October of UN Security Council sanctions designed to curb Iran's ballistic missile programme as part of a major 2015 nuclear agreement with world powers that has since unravelled.
'Impossible to hide' missile sales
Sir Richard Moore, the head of MI6, speaking alongside Mr Burns, signalled if Iran has started supplying ballistic missiles to Russia then it would be impossible to hide once used.
"If stuff comes on the battlefield, it will become very obvious, very quickly," he said.
"It explodes, it kills Ukrainian civilians, it destroys their infrastructure and… you have to remind yourself this is what Iran is choosing to do. It is choosing to help Russia to do these types of things."
It is not just Iran, North Korea has also bolstered shrinking Russian stockpiles with missiles and ammunition to be used in Ukraine.
China is another ally - with the power to provide potentially game-changing support.
Read more from Sky News:
Opposition leader flees Venezuela
Manhunt after cars shot at in US
But Mr Burns and Sir Richard said they had not yet seen any evidence that Beijing was supplying the Kremlin with conventional military hardware - though they believe it is helping with so-called "dual-use" technologies that have military as well as civilian utility.
"I don't think either of us see direct evidence today of the provision of weapons and ammunitions from China to Russia for use in the war in Ukraine," Mr Burns said.
"But we see lots of things just short of that - duel-use items, the kind of things that have enabled [Vladimir] Putin, over the last 18 months or so, to significantly rebuild his defence industrial base and that poses a real danger."
West could relax Ukraine's weapon restrictions
If Iran's supply of ballistic missiles is confirmed, the US, the UK and other Western allies will have to retaliate, most likely with further sanctions.
Such a move may also harden resolve over whether finally to start allowing Ukraine to use Western long-range missiles - such as the British Storm Shadow cruise missile - against targets inside Russia.
Concerns about Moscow's response has until now prevented permission from being granted.
But Mr Burns indicated that Western allies should not balk at Russian intimidation over any perceived escalation.
"Putin is a bully," he said. "He is going to continue to sabre rattle from time to time. I don't think we can afford to be intimidated by that kind of rhetoric."