In the final days of his rule, Syrian President Bashar al-Assad complained to Iran's foreign minister that Turkey was actively supporting Sunni rebels in their offensive to oust him, two Iranian officials told Reuters.
Five decades of rule by the Assad family ended when he fled to Moscow, where the government granted him asylum. Iran has supported Assad in Syria's long civil war, and his removal from power is seen as a major blow to the Iranian-led "Axis of Resistance," a political and military alliance that opposes Israeli and American influence in the Middle East.
As rebel forces from Hayat Tahrir al-Sham (HTS), formerly affiliated with al-Qaeda, seized major cities and advanced on the capital, Assad met with Iranian Foreign Minister Abbas Araqchi in Damascus on December 2.
At the meeting, Assad expressed anger at what he said were increased efforts by Turkey to oust him, according to a senior Iranian official. Araqchi assured Assad of Iran's continued support and promised to raise the issue with Ankara, the official said.
The next day, Araqchi met with Turkish Foreign Minister Hakan Fidan to express Tehran's deep concern about Ankara's support for the rebels' advance.
"The meeting was tense. Iran expressed its displeasure with Turkey's alignment with the US and Israeli agenda and conveyed Assad's concerns," a second Iranian official said, referring to Ankara's support for the rebels and cooperation with Western and Israeli interests in targeting Iran's allies in the region.
Fidan, the official said, blamed Assad for the crisis, arguing that his inability to engage in genuine peace talks and his years of oppressive rule were the root causes of the conflict.
A Turkish Foreign Ministry source familiar with Fidan's talks said those were not Fidan's exact remarks, adding that Araqchi had not brought or conveyed any messages from Assad to Turkey, without elaborating.
Fidan told reporters in Doha on Sunday that Assad's regime had "had valuable time" to address Syria's existing problems, but has failed to do so, instead allowing a "slow disintegration and collapse of the regime."
Iran's Supreme Leader Ayatollah Ali Khamenei said Wednesday that Assad's overthrow was the result of a plan by the United States and Israel.
He said one of Syria's neighbors also played a role and continues to play it. He did not name the country, but he appeared to be referring to Turkey.
Turkey, a NATO member that controls territory in northern Syria after several cross-border incursions against Syrian Kurdish militias, has been a major backer of opposition groups seeking to oust Assad since the outbreak of the civil war in 2011.
Assad's fall has deprived Iran and its ally, the Lebanese group Hezbollah, of a vital ally. Tehran's ties to Damascus have allowed Iran to extend its influence through a land corridor from its western border through Iraq and into Lebanon to supply weapons to Hezbollah.
Iran spent billions of dollars supporting Assad during the war and deployed its Revolutionary Guard in Syria to keep its ally in power.
"Hezbollah" has also played a major role, sending fighters to support him, but has had to send them back to Lebanon in the past year to fight a bitter war with Israel - a diversion that has weakened the Syrian government's lines.