Members of Syrian Democratic Forces (SDF) stand together near Baghouz, Deir Al Zor province, Syria, Feb. 11, 2019.
Members of Syrian Democratic Forces (SDF) stand together near Baghouz, Deir Al Zor province, Syria, Feb. 11, 2019.

The U.S.-led coalition in Syria says it carried out an airstrike against a former mosque in the last Syrian stronghold held by Islamic State fighters.

A coalition statement said the strike in Baghuz took place Monday, and was done in support of the Syrian Democratic Forces (SDF), a Kurdish-led anti-Islamic State coalition that is fighting the militants on the ground.

"This mosque lost its protected status when ISIS deliberately chose to use it as a command and control center," said Maj. Gen. Christopher Ghika, a British officer who serves as the coalition's deputy commander.

The U.S.-backed SDF is closing in on Islamic State fighters in Baghuz, located in the eastern Syrian province of Deir el-Zour.

Baghuz, Syria

"We have captured a radius of about 500 meters, and our fighters are advancing into the city," an SDF commander told VOA from the battlefield. "All civilians have already left this part of Baghuz. There are only IS fighters inside the town," he added.

U.S. officials say IS fighters in the town have been surrounded from all sides.

"The enemy is putting up a tough fight with a lot of foreign fighters with nowhere to go," coalition spokesman Col. Sean Ryan said. "The weather has not been great, which slows progress, and the SDF has to back clear the areas, as well. So, hopefully this month."

WATCH: US-backed forces close in on Islamic State

The anti-IS campaign has cleared nearly all territory once held by Islamic State in Syria since 2014.

The U.S.-led coalition is providing air and artillery support as SDF fighters continue to advance.

"The U.S. air support is very helpful in this offensive. It will also help us take over the remaining territory within days," said an SDF fighter, who is participating in the battle and did not want to be identified for security reasons.

The remaining IS fighters have no intention to surrender, local sources said.

"I don't think the battle will be over in a few days as many are predicting," said Ivan Hasib, a Syrian reporter who is embedded with the SDF in Baghuz.

"It will take at least two weeks before ISIS fighters are cleared," he said using an acronym for Islamic State.

Hasib added that "last week, [IS] refused an offer to surrender, which means that they have chosen to fight to the death. This has become more obvious in the past two days, as they are intensifying suicide attacks against SDF."

Surprise attacks

Local military officials say Islamic State relies on surprise attacks in a bid to slow the SDF offensive.

"This morning, [IS] terrorists attempted to wage surprise attacks in order to prolong the battle. But our forces and the U.S.-led coalition are present everywhere in the vicinity," Mustafa Bali, an SDF spokesman, told VOA on Monday.

There are also concerns that IS militants are using civilians as human shields to hamper the progress of U.S.-backed forces into the city.

WATCH: SDF operation in Syria

"The only thing that slows our advance is the presence of civilians. So far, 35,000 people have fled Baghuz. Just today, 1,500 civilians left the city. There are still large numbers of civilians stranded inside Baghuz. This is a real challenge for us," Bali said.