The Islamic State (ISIS/ISIL) has reportedly riddled its last sliver of territory in Syria along the Iraqi border with defensive tunnels, human shields, and mines, effectively hindering the U.S.-backed Syrian Democratic Forces (SDF) ongoing efforts to capture the pocket of land and and preventing them from declaring the group’s territorial defeat.

“It is expected that there are still undiscovered tunnels, even rooms underground,” said Mustafa Bali, a spokesman for the Kurdish-led SDF alliance told Reuters. “This creates a military problem for us.”

Referring to the number of ISIS jihadis, he noted, “There could be more than 1,000. They are all foreigners.”

“They are very fierce and professional, with high levels of experience. These are the elite fighters of Daesh [ISIS] who have gathered here from all over the world,” Bali added.

Abdel Karim Omar, a Kurdish foreign affairs official, told the Agence France-Presse (AFP) agency the SDF expects to announce the end of the territorial caliphate “in the next few days.”

“But this does not mean that we have eliminated terrorism, which must be eradicated at the roots,” he said.

The SDF has warned that ISIS has sleeper cells across Syria, adding that al-Qaeda in the country is also growing stronger.

SDF fighters have managed to reduce the so-called caliphate that once sprawled over nearly a third of Syria and Iraq to a hamlet of tents atop a network of tunnels and cave in the Syrian village of Baghouz where up to 1,000 mainly foreign jihadis are refusing to surrender and are using civilians as human shields.

Reuters reports:

The Syrian Democratic Forces (SDF) militia has surrounded the militants at the village of Baghouz near the Iraqi border and is trying to complete an evacuation of civilians from the tiny area before storming it or forcing a surrender.

Throughout its steady advance across the Syrian stretch of Islamic State’s self-declared caliphate, the SDF has been slowed by the group’s extensive use of tunnels and human shields – tactics it says are still being deployed in Baghouz.

“We will not end our moral victory over Daesh with a massacre,” the SDF spokesman told Reuters. “Whatever the price and whatever we can do we will work to evacuate the civilians. After that, the attack. There are two options: surrender or war.”

On Monday, the U.S.-backed Kurdish-Arab SDF alliance evacuated 46 truckloads of men, women, and children from ISIS’s last redoubt as part of efforts to clear the area of civilians before storming the region.

“According to what we heard from those who have left, there are nearly 5,000 people still inside,” Bali told AFP.

Citing the state-run Syrian Arab News Agency (SANA), the Associated Press (AP) also notes that the Islamic State (IS) has left behind land mines — including one that killed more than 20 people in Syrian on Sunday — in territory outside its last stronghold in Baghouz.

“IS has been driven out of virtually all the territory it once held in Syria and neighboring Iraq, but the extremists left behind countless bombs and booby traps, and large areas have yet to be cleared”, AP notes.

Last week, U.S. President Donald Trump’s administration announced that it would leave behind a residual American military presence in Syria to ensure ISIS lasting defeat and deal with other threats.

President Trump in December announced plans to pull out U.S. troops from Syria, stressing that the 5,000 American service members in neighboring Iraq would be able to go into the country if necessary.

Despite the near complete fall of ISIS’s territorial caliphate, the U.S. military and intelligence community warn that the group still remains a threat in Iraq and Syria and beyond, noting that the group has gone underground and is employing guerrilla tactics.

The SDF spokesman told Reuters an estimated 20,00 people had left ISIS’s last pocket of territory in recent weeks.

“Some of the fighters have attempted to slip out with them, and the SDF has set up screening points to vet everybody leaving the enclave,” Reuters reveals.

“However, Bali said it was hard to predict how many non-combatants remain inside the pocket and that although sources inside Baghouz have said there may be 5,000 civilians, previous estimates have turned out to be wrong,” it adds.