Iran has provided military support to Syrian government forces through more than a decade of civil war.
Near the start of the Syrian civil war, it was reported that then-Iranian President Mahmoud Ahmadinejad had personally sanctioned the dispatch of officers from the Iranian Revolutionary Guards to Syria to fight alongside Assad’s troops.
Ali Akbar Velayati, a top aide to Iranian Supreme Leader Ayatollah Ali Khamenei, made clear several years ago that Iran would withdraw its “military advisers” from Syria and Iraq only if their governments wanted it to.
Iran's President Ebrahim Raisi visited Damascus last year and headed a "high economic-political delegation".
However, the source told AFP on Wednesday that a series of strikes targeting its commanders in recent months has prompted a reshaping of Iran’s presence in Syria.
"Iran withdrew its forces from southern Syria," including both Quneitra and Daraa provinces, which abut the Israeli-annexed Golan Heights, the source close to Hezbollah said.
However, Iran still maintains a presence in other parts of the country, the source added.
Recent months have seen a series of strikes on Iranian targets in Syria, widely blamed on Israel, culminating in an April 1 strike that levelled the Iranian consulate in Damascus and killed seven Revolutionary Guards, two of them generals.
That strike prompted Iran to launch its first-ever direct missile and drone attack against Israel on April 13.
According to the source close to Hezbollah, Iran had already begun drawing down its forces after a January 20 strike that killed five Revolutionary Guards in Damascus, including their Syria intelligence chief and his deputy.
The Syrian Observatory for Human Rights, a Britain-based organization affiliated with the Syrian opposition, said Iranian forces had withdrawn from Damascus and southern Syria.
Iran has said repeatedly that it has no combat troops in Syria, only officers to provide military advice and training.
The Observatory, however, says as many as 3,000 Iranian military personnel are present in Syria, supported by tens of thousands of Iranian-trained fighters from countries including Lebanon, Iraq and Afghanistan.