Islamic State fighters are resorting to producing acrid smoke and leveling suicide attacks to hamper the advances of the U.S.-backed forces on their last stronghold in eastern Syria, eyewitnesses and sources on the ground tell VOA.

In an attempt to make one final stand in the Syrian town of Baghuz, IS fighters are now burning tires to produce smoke to prevent U.S.-led airstrikes and have intensified suicide attacks against U.S.-backed Syrian Democratic Forces (SDF), local sources said.

The IS tactics have slightly slowed progress of the U.S.-backed forces into Baghuz, SDF officials said.

Baghuz, Syria

"Unlike previous battles, where [IS] terrorists would just retreat, the Baghuz battle is a life-or-death matter for them," said Mushin Khalil, a Syrian reporter covering the battle on the ground.

Khalil said at least 14 SDF fighters were killed Tuesday in an IS counterattack that involved a suicide bomber.

There are an estimated 1,000 IS fighters inside Baghuz who are refusing to surrender, Kurdish military officials told VOA.

Lilwa Abdullah, a spokeswoman for the anti-IS campaign in eastern Syria, told Arta FM, a local radio station, that U.S.-backed forces on Tuesday arrested a significant number of IS fighters on the outskirts of Baghuz.

WATCH: IS Using Suicide Attacks, Fires to Slow Syrian Advance

US account

U.S. officials say IS fighters in the town are now surrounded.

"The enemy is putting up a tough fight with a lot of foreign fighters with nowhere to go," coalition spokesperson Col. Sean Ryan told VOA via email Monday.

He added that the forces hope to take the area "this month," saying their progress has been slowed by the weather and SDF forces having to clear areas once they have been taken.

Located near the Iraqi border, Baghuz is the last stronghold held by IS extremists in Syria.

SDF commanders

The battle to retake Baghuz from IS militants began over the weekend as the Kurdish-led SDF advanced on IS with the help of U.S.-led coalition airstrikes.

"Today we have received orders to use heavy weaponry and mortars," Shervan Ahmo, an SDF commander, told VOA on Tuesday. "As you can see, we are at the first frontlines. Fighting continues."

According to another SDF commander, IS now controls only 2 square miles at the center of Baghuz.

"All civilians have left the town. Those who have remained in this area are [IS] terrorists and their families," SDF commander Adnan Afrin told the Kurdish news agency Hawar.

Coalition airstrikes are more effective at night, which allow SDF fighters to inch closer to the center of the town, military officials said.

Since the beginning of the Baghuz battle, at least three airstrikes reportedly have hit IS targets inside the town.