OUTSIDE BAGHOUZ, Syria — Fighters with the US-backed force battling the Islamic State group in eastern Syria advanced on two fronts Saturday as the extremists used snipers and booby traps to slow the push on the last area they control, a spokesman for the group said.

Mustafa Bali of the Kurdish-led Syrian Democratic Forces tweeted that “heavy clashes” were taking place in the area on the east bank of the Euphrates River.

Zana Amedi, an SDF commander, told The Associated Press that “an active ground force” is advancing into IS-held territories as the extremists resort to sniper fire and booby-traps.

Two helicopters for the US-led coalition were seen circling the area of fighting around noon Saturday. A loud explosion later was heard from a distance and thick black smoke billowed into the sky, apparently a coalition airstrike.

The SDF on Friday evening resumed military operations to liberate the last piece of territory held by IS in the province of Deir el-Zour after evacuating thousands of civilians and hostages who had been besieged inside.

The military campaign to uproot the militants from the eastern banks of the Euphrates River began in September, pushing them down toward this last corner in the village of Baghouz, near the Iraqi border. The military operation was halted on Feb. 12 as the SDF said a large number of civilians and hostages were holed up in the territory, which sits atop caves and tunnels where they had been hiding.

By Friday, more than 10,000 civilians had left the IS held area and the extremists released some SDF fighters they had taken prisoner in earlier battles.

“We expect it to be over soon,” Bali said.

Another SDF commander, Adnan Afrin, said “there are fierce battles” with IS fighters firing thermal missiles at advancing troops and using drones. Afrin said eight SDF fighters were wounded, some critically.

Afrin said the buffer area between IS and SDF had been closed after the SDF’s advance. He said there have been no suicide attacks but that some land mines went off.

The Britain-based Syrian Observatory for Human Rights, a war monitor, said 10 IS gunmen were killed in fighting in the Baghouz area. It added that Syrian government forces and their allies clashed with IS gunmen who tried to cross to the west bank of the Euphrates river leaving seven IS members dead.

Amedi, the SDF commander, said the Kurdish-led force cannot rely on airstrikes by the US-led coalition because IS gunmen are trapped everywhere “so if you just rely on airstrikes and then advance on the ground that will cause heavy casualties.”

“At least now, we are trying to advance on the ground with rare airstrikes,” he said. “Now it’s mostly clashes. There are almost no airstrikes this morning. There were few airstrikes in the morning and nothing else after that.”