A Syrian Democratic Forces fighter looks through the scope of his weapon in Tal Samin village, north of Raqqa, Syria, Nov. 19, 2016.
A Syrian Democratic Forces fighter looks through the scope of his weapon in Tal Samin village, north of Raqqa, Syria, Nov. 19, 2016.

U.S.-backed Syrian Democratic Forces have made significant advances in their march toward the city of Raqqa, the Islamic State group's de-facto capital in Syria, an SDF spokesperson said Thursday.

The gains came in the second phase of an offensive against IS militants in Raqqa province.

A critical round of fighting lies ahead, aimed at seizing control of an economically and strategically important dam on the Euphrates River, before the SDF fighters can reach their ultimate target, the city of Raqqa itself.

SDF fighters have liberated 97 villages in the western part of Raqqa province in the past 10 days, said Jihan Sheikh Ahmed, a spokeswoman for the SDF offensive, dubbed "Rage of Euphrates."

"We have thus far liberated 1,300 square kilometers in western Raqqa," she told reporters at a news conference in a recently liberated village.

WATCH: US-backed Forces Advance on IS in Western Raqqa

Baath Dam is next target

The SDF, a coalition of Kurdish and Arab forces, launched its Raqqa offensive in early November, routing Islamic State fighters from the northern part of the province.

The alliance says it intends to liberate the strategic Baath Dam — a large hydroelectric power facility — 22 kilometers upstream from Raqqa city that supplies electricity to much of northern Syria. 

The dam, which IS has controlled since 2014, also is a vital source of irrigation water to the fertile region around Raqqa. Abdulqadir Huwaidi, an SDF commander, said his goal is to seize the dam to help local farmers, and to do it quickly, to reduce the chances that Islamic State extremists could sabotage the facility.

REUTERS Return of child and mother to Hisha, Syria
FILE - A woman carries a child as they return with others to the town of Hisha, after the Syrian Democratic Forces (SDF) took control of the area from Islamic State militants, in the northern Raqqa countryside, Syria, Nov. 14, 2016.

US, French forces aid SDF

Commanders on the ground who requested anonymity said there are fears that IS could be planning to blow up the 14-meter-high dam and cause a catastrophic loss of life.

Seizing control of the dam is an extraordinarily important goal, one commander told VOA by telephone, and American and French special forces are fighting alongside SDF in the area.

The U.S. recently announced it has assigned another 200 troops to Syria to train and advise local fighters battling IS, joining 300 American fighters already authorized to operate in Syria.

The ongoing offensive consists of two major front lines where SDF units, with the help of U.S. air support, are approaching Raqqa from the west, attempting to encircle the city and cut a highway link between Raqqa and the eastern city of Deir Ezzor, another IS stronghold.

Aiming to 'suffocate' IS

"Control of the dam and the highway would suffocate [Islamic State] economically and logistically," said Mahmoud Bali, a VOA Kurdish reporter who is embedded with the SDF.

Despite the recent territorial gains, the operation is becoming increasingly costly for the advancing SDF forces, due to landmines and improvised explosive devices left by IS fighters as they retreated. Two suicide car-bomb attacks in western Raqqa this week are believed to have killed at least a dozen SDF fighters.

When their imminent objectives have been met, commanders said, the SDF offensive will pause before undertaking the climactic major offensive on IS inside Raqqa.