Russia watches as ally Iran edges closer to collapse. Here's why it matters for Moscow

As Iran's future hangs in the balance as civil unrest gathers steam, its powerful ally Russia can do little but watch and wait as the U.S. ponders its next move against the Islamic Republic.

U.S. President Donald Trump has not ruled out using military strikes against the conservative religious regime that has ruled Iran since 1979. On Tuesday, he repeated that threat, warning the U.S. would take "very strong action" if Iran executed arrested protestors. Trump has already said any country doing business with Iran would be hit with a 25% tariff.

Russia will be focused on how events unfold in Iran given Tehran's position as a key strategic, military, economic and trade partner for Moscow in the Middle East.

The prospect of another ally falling in the Middle East will be a worrying one for Moscow, particularly after it has seen its alliances with Venezuela, Syria, and the Caucasus upended recently, denting its power and influence abroad.

"Moscow sees the potential loss of Iran as a much more significant risk to both its regional national posture than it saw the loss of Syria, Venezuela, or arguably its influence in Armenia over the last few years," Max Hess, founder of political risk consultancy Enmetena Advisory, told CNBC Tuesday.

"The reason for this is because Iran is itself a regional power projector, which offers Russia a platform to build alliances and expand its own influence," he said.

Mario Bikarski, senior analyst of Europe and Central Asia at Verisk Maplecroft, agreed that any regime collapse would be worrying for Moscow as it would represent another loss of power and influence, but could also unleash wider regional instability in the Caucasus region that separates Russia and Iran.

"There have been Iranian protests in the past, and Russia has always looked at them but never reacted, because they probably hoped that the Iranian regime will be able to withstand the pressure. But [this time] the pressure has been building up, and it's not only domestic, it's also external," he told CNBC Tuesday.

"Should the Iranian regime fall, Russia would probably have to scramble and find new ways to ensure that instability does not reach its borders, and also that it's maintaining some influence in the region," he said.

If a leadership vacuum emerged in Iran and rival factions vied for power, leading to further violence and unrest, that would mean "big security trouble for Russia and for a lot of other countries in the region," Bikarski warned.

Neither the Kremlin nor Russian President Vladimir Putin have commented on the events unfolding in Iran, although a muted response from Russia's leadership is not uncommon when it's trying to gauge the outcome of a particular event and how its strategic interests are impacted.

Russian state media has downplayed coverage of the protests in Iran, but Sergei Shoigu, the secretary of Russia's Security Council, decried on Monday what he described as "attempts by foreign powers to interfere in Iran's internal affairs," echoing Iranian accusations of Western interference.

A shared anti-Western ideology has been another bonding factor for Russia and Iran, as have international sanctions, which meant that Iran was one of the few international partners that Moscow could rely on for military hardware help after it invaded Ukraine in 2022.

The relationship has significantly deepened during the war, with Iran supplying Russia with "Shahed" attack drones and, allegedly, missiles, ammunition, and artillery for use in the war. Tehran admits it supplied drones to Russia but said it did so before the war.

In return, Iran reportedly received military technology and intelligence from Russia, as well as funding for its space and missile programs. Tehran was also believed to have coveted Russian Su-35 fighter aircraft and S-400 air defense missile systems, but it's unclear whether it ever received these.

One of the clearest signs that the alliance was more nuanced than it initially appeared, however, was when Russia stood back during heightened tensions between Iran and Israel, and amid 12 days of U.S. and Israeli air strikes on Iranian nuclear facilities.

Analysts told CNBC at the time that Russia was likely unable to support Tehran militarily — given its operations in Ukraine — but that it was also unwilling to support Iran as any direct conflict with the U.S. and Israel would be highly dangerous and damaging to Russia.

Moscow's standoffish stance was likely a wake-up call to Tehran's leadership about the limits of its alliance with Putin — limits that were being seen today too, analysts said.

"There is absolutely nothing meaningful that Russia can provide the Iranian regime to save it. It's too late, and I am not even sure the opportunity to aid the regime domestically ever existed since the Iranian people rose up," Bilal Saab, associate fellow in the Middle East and North Africa Programme at Chatham House, told CNBC Tuesday.

"The idea that Russia will come to Iran's aid or provide significant military expenditure to try to prop up the regime ... is very unlikely," Hess noted.

"Russia prioritizes its own interests ... and doesn't really believe in alliances, at least under Vladimir Putin, only ways to project power."

That is something that the Kremlin would be planning to do in the event of regime change in Iran, Bikarski said.

"Russia would try to re-engage with whoever succeeds the Islamic Republic, and would and try to ensure that their interests are shared with whatever new government takes form," he noted, with the alternative being that Russia is "completely pushed out of the Middle East."

That scenario, he said, would be highly undesirable for Russia.

"While it doesn't have the capacity right now to project power militarily or have a very strong trade relationship, it still wants to be seen as a partner in that region and would not like to relegate all of its influence to the United States voluntarily."