Islamic State militants are preventing more than 1,000 civilians from leaving a tiny area still held by the extremist group in a village in eastern Syria, a spokesman for the U.S.-backed Syrian militia fighting the group said on Sunday.

  “Regrettably, Daesh have closed all the roads,” Mustafa Bali, a spokesman for the Kurdish-led Syrian Democratic Forces, told The Associated Press, referring to IS by its Arabic acronym.

SDF officials have said the extremists are hiding among civilians in a tented village and using a network of caves and tunnels. IS, which once ruled a proto-state in large parts of Syria and Iraq, is clinging to an area less than a square kilometre in the village of Baghouz, in eastern Syria.

The extremists may include high-level commanders, and could be holding hostages among those trapped inside.

Occasional coalition airstrikes and clashes continue inside the village of Baghouz. Artillery rounds were meant to clear land mines for the SDF fighters to advance. SDF commanders say the end of IS’ self-declared caliphate is near.

“We will very soon bring good news to the whole world,” Ciya Furat, an SDF commander, said Saturday at a news conference at the al-Omar Oil Field Base, miles away from Baghouz in the Deir el-Zour province.

The capture of the last pocket of territory held by IS in either Syria or Iraq would mark the end of a devastating four-year global campaign to end the extremist group’s so-called caliphate.

At the height of their power in 2014, the extremists controlled nearly a third of both countries.

But experts and US Defense officials warn that the group still poses a major threat and could regroup within six months if pressure is not kept up.