As the fighting in Idlib rages, Turkey has ramped up weapons transfers to mainstream opposition and Ankara-backed groups in the area in a bid to warn the Syrian regime and Russia off from an all-out offensive.
With Russian backing, the regime has expanded its month-long aerial and ground assault on the last rebel-held territory in north-west Syria. While much of the territory is held by former Al Qaeda affiliate Hayat Tahrir Al Sham, there are still a number of Turkish supported and independent Free Syrian Army backed groups operating further north near the border region.
Syrian President Bashar Al Assad launched the assault last month, saying rebels had breached an existing ceasefire, triggering a civilian exodus by bombarding Idlib and adjacent areas. It has been the biggest escalation since last summer between Assad and his enemies in the province and a belt of territory around it.
A push that Damascus had hoped would allow them to snatch key territory on the edge of Idlib has quickly deteriorated for the government. They have seen a reverse of gains and the loss of a large quantity of arms captured in militant counterattacks.
An Ankara-backed rebel grouping called the National Army, which operates in north-western border areas near Turkey, said it has been allowed to join mainstream rebel factions along the front lines.
“Large numbers of our fighters have joined with all their weapons to repel the assault,” said Major Youssef Hamoud, its spokesman.
The rebels’ readiness to put aside differences that once led to bloody internecine fighting has united militant Islamists and mainstream rebels for the first time in years.
A Western security source told Reuters news agency that Washington has given the green light to the Turkish-backed mainstream rebels to use the TOW missiles, which had been in storage in the latest campaign.
The TOW missile had been the most potent weapon in the arsenal of rebel groups battling forces loyal to Syrian President Bashar Al Assad during the eight-year conflict.
Until 2017, Western and Arab opponents of Assad worked under a CIA-led programme to provide military support and training – including on TOW missile systems – to moderate rebels. In 2017, it was suspended after President Donald Trump took office.
In the early hours of Sunday, a Turkish military convoy arrived at a base in northern Hama near rebel-held Jabal Al Zawiya, which Russian and Syrian jets have been pounding for weeks, a rebel and a witness said.
The delivery of dozens of armoured vehicles, rocket launchers, anti-tank guided missiles and TOW missiles, helped roll back some Syrian army gains. Rebel groups successfully recaptured the strategically-located town of Kfar Nabouda on May 22, one senior opposition figure said.
The retreat from Kfar Nabouda was an upset to the Russian hopes for a speedy military campaign to gain another slice of heavily populated Idlib province.
Ankara stepped up supplies in recent days after failing to persuade Russia to end its escalation to avert a major displacement of refugees pouring into Turkey, two senior opposition figures said.
In doing so, Turkey signalled its readiness to preserve its influence in north-western Syria, where it has beefed up its troop presence in a dozen military bases that were set up under a de-escalation deal with Russia, a senior rebel commander said.
The US, which has criticised Russia's latest campaign and urged a ceasefire, also said it saw signs that Al Assad has used poison gas in the latest offensive.
"We do have numerous sources including interviews with those present during the attack that did report that a number of opposition fighters were taken to local hospitals and presented symptoms that were consistent with chemical exposure," State Department spokeswoman Morgan Ortagus told reporters.
Washington warned that it would respond “quickly and appropriately” if this were proven.
Mr Assad has denied such allegations throughout the war but previous uses have provoked limited strikes on the regime by US and allied forces.
A spokesman for the Turkey-backed National Liberation Front, Captain Naji Mustafa, did not confirm or deny any new supplies by Turkey, saying rebels had long had a big arsenal of weapons from anti-tank to armoured vehicles “alongside material and logistical support by our Turkish brothers”.
On Saturday, the Syrian army sent large troop reinforcements ahead of opening a new front, a source in touch with Syrian army commanders told Reuters.
The Syrian army said on Saturday it continued to intensify its attacks on what it called terrorist hideouts in the north-west.
There is a concern that the push not being as easy as Damascus had anticipated could bog the sides down into a prolonged battle that draws in further Syrian government-aligned forces and worsens the already deteriorating humanitarian situation. Over 3 million civilians are trapped in north-west Syria, many of whom have been displaced from other government offensives and agreed to be bussed to Idlib to escape. They now have nowhere to go.
Thousands have been displaced by the Russian-led bombing campaign that has hit hospitals, civilian homes and – according to reports – camps for the displaced.