AL-OMAR OIL FIELD BASE, Syria — Dozens of trucks arrived Tuesday at the outskirts of a besieged enclave held by the Islamic State in eastern Syria, signaling renewed efforts to evacuate hundreds of civilians trapped in the militants’ last patch of territory along the Euphrates River.

A spokesman for the U.S.-backed Syrian militia that is spearheading the fight against IS said a military operation aimed at ousting the extremists from the enclave will begin if they don’t surrender.

Such an operation would take place after separating or evacuating civilians from the militants, estimated to be about 300 combatants, said Mustafa Bali, the spokesman for the Syrian Democratic Forces.

Just before sundown Tuesday, more than 40 trucks headed toward Baghouz, the last village where IS militants are trapped with hundreds of civilians. There was no sign of the civilians returning by dark, and on the other edge of the IS-controlled territory, more than one airstrike hit, apparently increasing the pressure on those holding out. Gunfire echoed over the hills in the distance as soldiers from the SDF waited for the expected evacuation.

“We are working on either separating the civilians or evacuating them and raiding the place,” Bali said.

The Islamic State has been reduced from its self-proclaimed caliphate that once spread across much of Syria and Iraq at its height in 2014 to a speck of land on the countries’ shared border. In that tiny pocket, the militants are hiding among civilians in the shadow of a small hill, encircled by forces waiting to declare the territorial defeat of the extremist group.

Bali’s comments signaled an easing of a standoff that has lasted for more than a week. Nearly 20,000 civilians had left the shrinking area in recent weeks before the evacuation halted last week when the militants closed all the roads out of the tiny area.

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