An advance by the Assad regime forces against Daesh in northern Syria has opened a new link between regime-held areas in western Syria and the country's northeast held by YPG-dominated and U.S.-backed Syrian Democratic Forces (SDF), redrawing the map of the conflict near the Turkish border.

The advance, if sustained, could open a trade lifeline between the northeast, which holds 70 percent of Syria's oil and also includes rich farmland, and the west, where Syria's manufacturing and most of its population are based.

Northern Syria is one of the most complicated battlefields in the multi-faceted Syrian war that erupted in 2011.

The regime advance has begun just south of the town of al-Bab and has pushed forward into the territory expanding northwards, where Turkish forces and the Free Syrian Army (FSA) are currently waging Operation Euphrates Shield, which aims to carve out a buffer zone to keep Daesh and PKK-affiliated groups away from the Turkish border.

Regime government forces have now come to the edge of a swathe of territory controlled by the SDF, which has mostly avoided conflict with Damascus but is viewed by Turkey as an extension of the PKK terrorist group that has waged a three-decade insurgency on Turkish territory. The YPG, which is the armed wing of PKK's Syrian offshoot PYD, is the dominating force within the SDF. The YPG's critics have accused it of cooperating with Damascus in the Syrian civil war.

The spokesman for the SDF militia alliance said the regime army's advance would bring benefits to civilians in the area.

"On the trade front and on the civilian front it is seen as an excellent thing, because now there is ... a link between the entire northern rural area," spokesman Talal Silo told Reuters.

Now, he said, there was a direct route from the SDF-controlled town of Manbij to the city of Aleppo "via areas controlled by the SDF and areas controlled by the regime forces."

There was no immediate comment from the regime on its latest advances, but state media said the village of Fikha al Sagira was captured as the army expanded control of areas south of al-Bab.

The town fell to Turkey-backed FSA on Thursday, after months of heavy fighting against Daesh terrorists.

By taking control of Daesh territory south of al-Bab, the regime army is seeking to prevent any possible move by Turkey and the FSA to expand southwards.

However, regime forces and FSA elements have been involved in fierce clashes in villages southwest of al-Bab and its southern suburb Tadef as regime forces advanced to the northeast of Aleppo against Daesh. So far, a greater escalation had been stopped through the nationwide ceasefire between the regime and opposition groups devised by Turkey and Russia.

The FSA also said on Monday that they had captured a string of villages east of al-Bab.

The Syrian Observatory for Human Rights says the regime advance in the area is part of a bid to block Turkish-backed forces from expanding their zones of control in Aleppo province.

But regime troops are also trying to advance east to reach Daesh-held Khafsah, the main station pumping water into Aleppo city, Observatory head Rami Abdel Rahman said. Residents of the northern city have been had no water for 42 days, after Daesh cut the supply at Khafsah around 90 kilometers (55 miles) away.

SDF hails regime's advance

The Observatory said the regime army had captured some two dozen villages from Daesh, bringing it to the edge of SDF-held areas south of Manbij.

The SDF captured Manbij from Daesh last year with support from the U.S.-led alliance against the terrorist group, despite Turkey's warnings that it considers a PKK-affiliated force west of the Euphrates River to be a grave threat to its national security. In addition to al-Bab, Turkish leaders and officials have often cited Manbij as the initial goal of Euphrates Shield operation.

Spokesman Silo said residents of northeast Syria, who had previously depended on medical care in Aleppo and Damascus, would be able to do so again. "All these matters are in the interests of the citizen," he said.

The Assad regime still has footholds in YPG-dominated northeastern Syria in the cities of Qamishli and Hasakah. The YPG also controls part of the city of Aleppo, where regime forces and their allies defeated opposition groups in December.

The YPG forms the military backbone of three self-declared autonomous areas set up in predominantly Kurdish regions of northern Syria since the onset of the conflict in 2011.

Turkey's intervention has disrupted the YPG's plans to link up the two autonomous areas of northeastern Syria with the third one, which is located in northwestern Syria.

During their advance against Daesh, forces affiliated to the YPG also captured the predominantly Arab town of Tal Abyad, prompting protests from human rights groups upon their expulsion and the violent policies against local Arabs and Turkmens.

The main Syrian Kurdish groups and their allies want to preserve their autonomy in a new federal system of government for Syria. Bashar al-Assad's regime opposes the idea.

Regime airstrikes resume in Idlib, Daesh on the retreat in Palmyra

Further south, regime troops fought to within four kilometers of the ancient desert city of Palmyra, which Daesh recaptured in December.

"Regime forces speedily advanced around Palmyra, specifically from the northwest and southwest, capturing a string of hilltops that allow them to fire on the oil and gas fields in the area," Abdel Rahman said.

Syria's conflict began in March 2011 with protests against Bashar al-Assad's rule but has since spiraled into a multi-front war pitting regime forces, moderate opposition, extremist groups and PKK-dominated Kurdish groups against each other.

Regime air raids on the northwest province of Idlib killed at least 13 civilians overnight, the Observatory said. It had originally given a preliminary toll of 11 dead in the bombardment of Ariha.

Leith Fares, a rescue worker in Ariha, told AFP his team had pulled at least 20 wounded people from the rubble.

"We've been working since 3:00 am (0100 GMT) to rescue victims still under the rubble of two four-storey buildings that totally collapsed on the residents inside," he said.

"We're still looking for two families, estimated at eight to 10 members each, that are still trapped," Fares said.

The deaths come two days after 10 civilians were killed in regime air strikes on Ariha, held since spring 2015 by an anti-regime coalition dominated by extremist groups.

Idlib province has been battered by heavy air strikes in recent weeks, with intensifying raids by regime warplanes in particular, according to the Observatory.

It has also been rocked by infighting between moderate opposition groups and extremist factions, including Al-Qaeda's former Syrian affiliate, Fateh al-Sham Front.