For decades, Iran has expended much blood and money in support of Syria’s President, Bashar al-Assad, helping him survive a civil war that threatened his dynastic rule.

Iran operated military bases, weapons warehouses and missile factories in Syria, which it used as a pipeline for arming its militant allies across the region.

Now, just as Assad needs help to repel a rapid advance by rebel forces, Iran is heading for the exits. On Friday, the country started evacuating its military commanders and personnel, as well as some diplomatic staff, according to Iranian and regional officials.

It is a remarkable turnabout: Iran not only appears to be abandoning Assad, its closest Arab ally, but also relinquishing everything it had built and fought to preserve for 40 years in Syria, its main foothold in the Arab world.

Iran is unable to muster a defence of the Assad government after a damaging year of regional wars that began with the October 7 attack on Israel by Hamas, an Iranian ally.

After Assad was toppled by rebels on Sunday, Iran’s foreign ministry said that Syria’s fate was the sole responsibility of the Syrian people and should be pursued without foreign imposition or intervention.

“We will spare no effort to help establish security and stability in Syria, and to this end, we will continue consultations with all influential parties, especially in the region,” the foreign ministry added.

The foreign ministry said it expected ties between Tehran and Damascus to continue based on the two countries’ “far-sighted and wise approach”.

A collapse of Iran’s partnership with Syria would by all accounts reshape the balance of power in West Asia. The “axis of resistance” that Iran has formed with its militant allies in Lebanon, the Palestinian territories, Syria, Iraq and Yemen would be weakened. Israel and its Arab allies would be strengthened.

“For Iran, Syria has been the backbone of our regional presence,” Hassan Shemshadi, an expert on Iran’s proxy militant groups who was for years a documentary filmmaker on the battlefields of Syria, said in an interview from Tehran. “Everything that Iran sent to the region went through Syria. It is now extremely difficult to keep these channels open.”

Initially, the Iranian government was shocked at how quickly the rebels in Syria gained ground and the Syrian army abandoned its bases, according to three Iranian officials, two of them members of the elite Revolutionary Guards, and two prominent Iranian analysts close to the government.

By midweek, the mood had turned into full panic, the officials said, as the rebels were on a march that would hand them city after city, from Aleppo to Hama to Deir al-Zour and Daraa.

Publicly, Iranian officials vowed to remain fully committed to supporting Assad. But privately, as the rebels gained control over more and more territory where Iran and its proxy militias had reigned, they wondered if events were outpacing their ability to turn the tide, the officials said.

By the end of the week, several senior officials had made statements on social media that Assad’s ouster was seemingly inevitable and Iran’s setback monumental.

Although Iran’s foreign minister, Abbas Araghchi, who has travelled to Damascus, Baghdad and Doha, Qatar, for consultations on Syria, at first struck a defiant tone, he later said that Assad’s fate would be left to “God’s will”.

An internal memo from a Revolutionary Guards member that was viewed by The New York Times described the situation in Syria as “unbelievable and strange”. It is as if “Iran accepted the fall of Assad and has lost the will to resist,” the memo says.