Intelligence agencies of the United States and Saudi Arabia plan to allow more than 9,000 Daesh fighters leave the Iraqi city of Mosul and travel to eastern Syria where they will take part in a major offensive to recapture Deir ez-Zor and Palmyra among over things, an unnamed source in military and diplomatic circles in Moscow told RIA Novosti.

"American and Saudi intelligence services have reached an agreement to provide all militants a safe passage to leave the city with their families before" Iraqi security forces and their allies launch the operation to free Mosul, he suggested. The matter was ostensibly settled during the preliminary phase of the offensive.

When the Mosul campaign begins, "coalition warplanes will launch airstrikes solely against isolated and abandoned houses within the city," the source noted, adding that these targets have been chosen in coordination with the militants.

Daesh fighters, he said, will then move to Syria.

"More than 9,000 Daesh fighters from Mosul will be redeployed to eastern Syria to carry out a large-scale offensive which will involve among other things taking control over Deir ez-Zor and Palmyra," the source detailed.

For Washington, this plan, the source suggested, will be an attempt to diminish Russia's success in Syria. Moscow has been credited with helping the Syrian Arab Army turn the tide of war that has seen Damascus fighting against foreign-sponsored terrorist groups for more than five years.

"Apart from political dividends, the other goal of this operation clearly involves discrediting the achievements of the Russian Aerospace Forces. Surely, this is also an attempt to undermine [Bashar] al-Assad," the source said.

Senior officials at the General Intelligence Directorate, Saudi Arabia's primary intelligence, served as mediators between the US and the militants, the source said, adding that they will also guarantee that Washington delivers on the deal. He explained that a similar idea was previously employed in Fallujah.

Baghdad-led forces freed Fallujah in late June after a three-months-long siege.

Political analyst Alexander Perendzhiev doubted that this plan will work.

Daesh "has Iraqi roots; Mosul is their stronghold and they will clearly be unwilling to leave Iraq," he told RIA Novosti. "Mosul will probably remain in the hands of terrorists. Some of them will travel to Syria and the rest will pretend that they surrender."

The expert further said that the Democrats will try to claim any success in Mosul, whether perceived or real.