Bashar al-Assad fled the country on a midnight flight that disappeared from radar.
Sources in the region say the Syrian president's plane took off towards a Russian base in Syria, with US officials saying they believe he was heading for refuge in Moscow.
However there has been no confirmation of what happened after the flight took off, raising questions of his whereabouts.
A Syrian aeroplane took off from Damascus airport around the time the capital was reported to have been taken by rebels, according to data from the Flightradar website.
The aircraft initially flew towards Syria's coastal region, a stronghold of Assad's Alawite sect, but then made an abrupt U-turn and flew in the opposite direction for a few minutes before disappearing off the map.
The Telegraph could not immediately ascertain who was on board.
Two Syrian sources told Reuters there was a very high probability that Assad may have been killed in a plane crash as it was a mystery why the plane took a surprise U turn and disappeared off the map according to data from the Flightradar website.
"It disappeared off the radar, possibly the transponder was switched off, but I believe the bigger probability is that the aircraft was taken down..." said one Syrian source without elaborating.
Russia has long stood by Mr Assad in the face of the civil war since 2011, and on Sunday morning, its embassy in Egypt released a statement slamming the rebels, blaming the takeover on its arch enemy, the US.
"According to information from Syria, the capital of this Arab country has been captured by terrorists, who are backed by external forces led by the United States. They stubbornly want to destroy the Syrian state and destabilise the entire Middle East, bringing more suffering to the Arabs," the statement said.
Chris Doyle, a Syria expert and Director of the Council for Arab-British Understanding, said there are limited places for Mr Assad to hide.
"There are clear reasons to suspect Moscow and I'd probably put my money on that," he told The Telegraph. "He has to go somewhere that feels safe and where he won't be handed over to an international criminal court, a place that will protect him. In my mind, Moscow will be the one."
According to the UN, over the past ten years, an average of 84 civilians have been killed every day in direct connection to the war in Syria, by 2022, totalling an estimated 306,887 civilians.
The US State Department estimates that 1,400 people were killed in 2013 when the Assad regime launched rockets carrying the deadly nerve agent sarin into the Ghouta district of Damascus.
With Russia a key ally, along with Iran, in the civil war, Mr Assad has deep ties with Moscow.
"He had a few choices, Iran would be another, and others have talked about Dubai, but I'm not convinced by that," said Mr Doyle, who says that it would only have been in the final hours of the takeover that the decades-long leader would have believed that his reign was over.
Dubai reinstated relations with Syria, hosting Mr Assad in 2022, his first visit to an Arab country since the start of the war, and before the Arab League reinstated Syria's membership.
Through backdoor diplomacy, the UAE has long hoped to distance Mr Assad from Iran through building business ties with Syria, although US sanctions have hampered those efforts.
On Saturday, Bloomberg reported that Mr Assad had been in last-minute talks with the UAE to cut a deal to save him if he agreed to cut ties with Iran.
US President Joe Biden and his team were monitoring the "extraordinary events in Syria" and were in touch with regional partners, the White House said.