The Syrian army hit back after a major Isis counteroffensive yesterday, hours after a new ceasefire between government forces and Western-backed insurgent factions came into effect.

Troops regained several towns and an airbase overrun by Isis in Thursday’s counterattack along a 100-mile front stretching from Sukhnah, east of Palmyra, to the eastern city of Deir Ezzor.

The M20 motorway was reopened after B’ir Ghabaghib and al-Shoula were retaken with support from attack jets and helicopters.

Isis also briefly captured the T-3 airbase and oil pumping station south of Sukhnah, but were driven out within an hour.

The Kurdish-led Syrian Democratic Forces, which are supported by the US, defeated a smaller Isis offensive in oil-rich al-Shula, east of the Euphrates from Deir Ezzor.

On Thursday, an anonymous senior commander in the US-led Operation Inherent Resolve coalition told the AFP news agency that its next target was al-Mayadeen, 25 miles south-east of Deir Ezzor on the river’s west bank.

“There are a lot of folks in al-Mayadeen who plot external attacks on our homelands, on coalition homelands, so we can't allow it to remain an Isis sanctuary," he alleged.

But a coalition capture of al-Mayadeen would place more of Syria’s large gas and oilfields under US control and prevent government troops meeting up with their Iraqi allies on the eastern border.

Russian Foreign Ministry spokeswoman Maria Zakharova said reconnaissance images released by the Defence Ministry on Sunday had shown that US troops embedded with the SDF felt “completely safe” operating in Isis-controlled territory.

Russian Defence Ministry spokesman Major General Igor Konashenkov said the Pentagon had not yet commented on the aerial photos.

A new ceasefire took effect in north-western Syria at midnight on Thursday following an Ankara meeting between Russian President Vladimir Putin and his Turkish counterpart Recep Tayip Erdogan.

Syrian and Russian warplanes had blitzed targets in Idlib and neighbouring provinces since al-Qaida extremists carried out a sneak attack on Russian peacekeepers last week that the Kremlin accused Washington of orchestrating.