US-backed Arab and Kurdish fighters said on Friday they would launch an offensive "very soon" to oust ISIL from Syria's oil-rich Deir Ezzor province.
The strategic territory is also seen as a prize by advancing Syrian troops, but an agreement between regime ally Russia and the US-led coalition is expected to keep the rival assaults from clashing.
The Deir Ezzor Military Council (DEMC), a coalition of Arab tribes and fighters that belongs to the broader US-backed Syrian Democratic Forces, announced the upcoming offensive on Friday in north-east Syria.
"Our forces are preparing for the great battle of Deir Ezzor and unifying the tribes," said DEMC head Ahmad Abu Khawlah in Shadai, some 60 kilometres south of Hassakeh.
He said at least 1,500 tribal fighters had joined the DEMC.
"There is no specific timeframe for the battle, but it will be very soon," he said.
The SDF is currently waging a ferocious fight for Raqqa, ISIL's self-declared capital about 75km west of the administrative border with Deir Ezzor.
SDF fighters have seized some territory in Deir Ezzor province, but Russian-backed Syrian government forces have been making a mad dash towards the provincial capital of the same name.
Regime troops have swept across Syria's desert to break ISIL's two-year siege on tens of thousands of people trapped in Deir Ezzor city.
The US-led coalition has said that a "de-confliction line" has been set to prevent any "mishaps" between the two advancing forces.
Spokesman Colonel Ryan Dillon told journalists this month that the line "has been coordinated and de-conflicted, and has been placed between the SDF and the regime and the Russians and the US".
Abu Muhammad Al Shayti, who heads the DEMC's Shaytat tribal unit, said on Friday that his fighters "will not target Deir Ezzor city, but the province".
"Our forces are committed to what the coalition sees as fit - to fight Daesh only," he said.
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Read more:
[ What ISIL's rise in 2014 tells us about Al Qaeda's potential in Syria today ]
[ Syrian government takes last ISIL-held town in Homs ]
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ISIL has lost swathes of territory to US-backed forces in northern Syria and to Russian-backed Syrian troops in the country's centre and east.
Moscow has said the recapture of Deir Ezzor could mark the conclusion of the battle against ISIL.
And the US-led coalition's deputy head, British Major General Rupert Jones, said on Wednesday the final fight would probably take place in the stretch of border between Syria and Iraq.
"The expectation has always been that that would see Daesh increasingly squeezed into ... the middle Euphrates valley, and that is where the military defeat will be completed," Maj Gen Jones said.
