MOSCOW has sensationally raised its suspicions that Washington colluded with Isis to recapture the Syrian city of Palmyra, as reinforcements poured in yesterday to stem their advance.

Tadmur — the modern city on the site of the precious ancient ruins of Palmyra — fell at the weekend when Isis conjured up 5,000 fighters, overwhelming the 1,000 army troops and their Russian allies.

The city was liberated in March after falling to Isis in May 2015. The extremists destroyed many of the ancient relics at the Unesco world heritage site.

Yesterday the Syrian army ordered 2,500 reinforcements from Aleppo province to the Tiyas airbase west of Palmyra, where outnumbered troops beat back Isis attacks with the help of heavy air strikes.

Russian Defence Minister General Igor Konashenkov said on Monday night that the Wahhabi death cult had taken advantage of a pause in the US-backed offensive towards its stronghold of Raqqa by the Kurdish YPG militia.

And he added that thousands of the extremists had arrived “unhampered” from the Iraqi city of Mosul, the US-co-ordinated offensive having left a “back door” to Syria open for weeks until Shi’ite militia closed the gap.

“It is obvious that the terrorists concentrated near Palmyra were sure that the military action in Raqqa would not renew.”

Foreign Minister Sergey Lavrov said the brigade-sized force of terrorists had apparently crossed terrain patrolled by the US-led bombing coalition, which “makes one think that the whole has been orchestrated.

“I hope I’m wrong,” he added.