Syria conflict: Will Aleppo fall to Islamic State?
There are growing fears that Syria's second city, Aleppo, could be taken over by Islamic State (IS) as fighting to the north between government and rebel forces intensifies.
With the military being driven out of the adjacent province of Idlib by a newly-formed rebel alliance, the Army of Conquest, focus has shifted to the fate of Aleppo, an ancient trading hub near the border with Turkey that has been a battleground for the past three years.
IS fighters are reportedly heading towards the city, while the Syrian opposition and the US have accused the regime of helping the jihadists by carrying out air strikes on rebels fighting them, especially in the town of Marea, north of Aleppo.
The US has accused the regime of "avoiding [IS] lines", contradicting its claim to be fighting the group.
The US-led coalition fighting IS is focusing its attacks against the group in Iraq and in Raqqa in northern Syria, where the IS has established its headquarters.
Last month, both Syrian government forces and the coalition failed to stop hundreds of IS fighters from crossing almost 45 miles (70km) of desert to seize the ancient city of Palmyra.
There have been sporadic clashes between the government and IS, but the Syrian opposition accuses the regime of allowing IS into Palmyra and pulling out of the city and its ancient ruins, leaving tonnes of weapons that the radical group is now using.
The fear is that a similar scenario may take place in Aleppo. The city is divided between the government-held west and the rebel sector in the east.
The government also controls the area to the south of the city while to the east IS is in control, stretching to Raqqa province and nearly all of the oil-rich city of Deir al-Zour.
To the west of Aleppo, the area is still contested by both the army and rebel forces, where opposition fighters are besieging pro-government towns of Nubul and Zahra.
The focus now is on the north, a critical supply line to the rebels in Aleppo, and where the fighting has intensified.
The government has intensified its air strikes on rebel forces there while IS is advancing.
If the jihadists are victorious, they could control one of the main border crossings with Turkey, Bab al-Salam, which would be another source of funding for them.
This would also make Islamic State's presence closer to Turkey, itself accused by the Assad regime of supporting IS, which Ankara denies.
The Army of Conquest says it is determined to defend Aleppo and prevent both IS and the government from controlling it. But the battle is going to be fierce and bloody.
'The world will be surprised'
President Assad has argued since the start of the uprising that there is no real call for change in Syria, constantly describing the armed opposition as a "terrorist" Sunni extremist movement that must be fought.
When IS first appeared in 2013 in Raqqa, government forces hardly attacked the group, which helped it grow.
Barrel bombs and air strikes continue to target all other opposition groups in Syria, with most of the victims civilians.
Mr Assad is sending a message to the West that if he was overthrown, the only alternative would be fundamentalist groups like IS.
Developments in the north and the withdrawals from both Idlib and Palmyra suggest the president might be preparing for a divided Syria in which he kept control of Damascus and the Mediterranean cost in the west, leaving the north to the jihadists.
But at the same time, the regime feels embarrassed about the rebel advance. It could not justify the loss of Idlib to its loyalists internally nor to its allies, especially Iran, which has sent military personnel and arms to help.
And as the rebels get closer to the regime's coastal stronghold of Latakia, Tehran looks increasingly unwilling to rely on Mr Assad's forces.
The head of the Iranian Revolutionary Guards' elite Quds Force, Qasem Soleimani, is reported to have recently visited Latakia, and declared: "The world will be surprised by what we and the Syrian military leadership are preparing for the coming days."
The pro-Syrian Lebanese newspaper, Assafir, has said almost 20,000 fighters from Iran and Iraq have arrived in Syria to fight for Idlib.
This is in addition to the fighters from those countries already on the ground, indicating how the regime is growing weaker by the day and how strategic decisions are increasingly made abroad.