• Russia carried out airstrikes in Syria after rebels launched an offensive against the Syrian government.
• Russia and Iran have supported Syrian President Bashar Assad for years.
• Here's why Syria is so important for both Moscow and Tehran.

Russia has been carrying out airstrikes on Syrian rebel fighters who are advancing through the country as part of an offensive that has seen them seize control of Aleppo, one of Syria's largest cities.

The surprise offensive, led by Islamist militants from the opposition group Hayat Tahrir al-Sham, marks the most significant escalation in the Syrian civil war in years — and the outcome has serious implications for both Russia and Iran.

Russia's gateway to the Mediterranean

Syria holds strategic importance for Moscow and Tehran, which have both supported Syrian President Bashar Assad's embattled regime.

For Russia, which operates two major military bases in the country — the Hmeimim airbase and the Tartus naval base — Syria offers a key foothold in the region, giving its forces crucial access to the Mediterranean Sea and a launching pad for operations in Africa.

Russia has sought to extend its influence across the Middle East and Africa in recent years as a counterweight to the US, forging closer ties with key Middle Eastern players like Iran and Saudi Arabia and reportedly providing African governments with security assistance through the Wagner mercenary group.

Natasha Hall, a senior fellow with the Middle East Program at the Center for Strategic and International Studies, told Business Insider that Russian President Vladimir Putin cannot afford to lose a Russia-friendly government in Syria for fear of losing the airbase and warm water port crucial to maintaining its influence in the region.

"It's used that port and the base as a launching pad to move into Africa," Hall said. "At one point, there were at least 30 Russian warships in the Mediterranean, whereas just a few years prior, there were none."

Zineb Riboua, a research fellow and program manager at the Hudson Institute's Center for Peace and Security in the Middle East, said losing Syria would be "a big deal for Russia."

"Most of its plans in the Sahel and Libya revolve around supporting Russia's access to the Mediterranean, without a strong Russian military base in Syria, all of Putin's plans collapse," Riboua wrote on X.

Putin's support for Assad helped boost his popularity in Africa, Riboua continued, adding that losing Syria would "make Putin not just look weak, but look unreliable to many African countries that rely today on Wagner."

Iran's network of proxies

Syria also provides Iran with access to the Mediterranean via a land corridor that extends from Tehran through to Baghdad, Damascus, and Beirut, connecting its proxies in the region.

"For Iran, Syria is absolutely essential in order to maintain its proxy network," Hall said. "It now has this unimpeded route from Tehran all the way to Lebanon."

Syria is particularly important for Iran's ability to support the Lebanese militant group Hezbollah, which for over a year has been embroiled in conflict with Israel. Israel has recently thrown this top Iranian ally into disarray, killing its longtime leader and wounding thousands of its fighters with exploding pagers and walkie-talkies. A cease-fire agreement was reached between Israel and Hezbollah last week.

"Iran is deeply invested in Syria with dozens of military bases and other facilities because the country is critical to Tehran's support for Hezbollah," wrote Steven Cook, the Eni Enrico Mattei senior fellow for Middle East and Africa Studies at the Council on Foreign Relations think tank.

Syria provides Tehran with a place to manufacture weapons and a route to transport them, as well as a command post for Iranian commanders who work with Hezbollah, Cook said.

But Israeli strikes on the militant group have impacted Iran's corridor and put its position in the region under pressure.

Tehran may, therefore, see the Syrian conflict as a way to reimpose itself in the region, Riboua said in another post on X.

"Weakened in Lebanon and Gaza, Iran now views the conflict in Syria as an opportunity to reassert its influence by joining the Assad regime against its opposition," Riboua said. "Tehran likely sees this renewed involvement as a chance to restore its legitimacy and strengthen its control over its proxies."

Latest conflict is 'no surprise'

Russian ties with Syria trace back to the Cold War-era when Moscow supplied arms to the country.

The two countries grew closer under the leadership of Putin and Assad, as the former sought to expand and defend Russian interests in the Middle East.

In 2015, this resulted in Russia directly intervening in the country's civil war, which began in 2011, to prop up Assad.

Over the following years, Moscow steadily built up its military presence in Syria, and by 2018, the Russian Ministry of Defense said that more than 63,000 Russian troops had "received combat experience" in the country.

But following Russia's full-scale invasion of Ukraine in February 2022, Moscow's Syrian operations were put on the back burner, and it reportedly redeployed some troops, mercenaries, and military equipment from Syria to Ukraine.

Iran and Syria, meanwhile, have had strong relations since the 1979 Iranian revolution.

Iranian troops are also reported to have fought alongside Syrian government forces in 2015.

But like Russia, Iran's priorities have shifted in recent months, with Tehran locked with Israel in a series of escalating long-range strikes.

For the US, that meant the latest offensive seemingly came as no great shock.

Speaking to NBC News, national security advisor Jake Sullivan said that Assad's three key backers, Iran, Russia, and Hezbollah, had all "been distracted and weakened by conflicts elsewhere."

"So it's no surprise that you see actors in Syria, including the rebels, try to take advantage of that," he added.

For Russia and Iran, the fall of Aleppo will nevertheless come as a humiliating blow, Hall said.

It shows "how weak their ally is, even after 13 years of war," she added.