The Pentagon highlighted Friday a recent victory against the Islamic State group in Syria as evidence its tactical plan to defeat the jihadists is working.

The US-led coalition's strategy in Syria and Iraq is to bomb IS targets using drones and warplanes, while also deploying specialized commandos on the ground to train and arm local anti-IS fighters.

In Syria, about 50 US commandos are working with anti-IS fighters including a largely Kurdish group called the Syrian Democratic Forces.

In perhaps the SDF's most significant victory yet, the local fighters between February 15 to 22 encircled the town of Al-Shadadi in Hasakeh province, then moved in and recaptured it from the jihadists.

The SDF were backed up by US-led bombardments, and US special operations forces were in the vicinity offering tactical advice, calling in air strikes and helping with logistics and resupplies, Baghdad-based military spokesman Colonel Chris Garver said in a phone briefing.

About 20 SDF fighters and 260 IS members were killed in the battle, which saw heavy IS resistance outside Al-Shadadi but less in the town itself.

"Not only did the advancing fighters have to contend with remnants of Daesh fighters, but they also have to contend with significant amounts of IEDs throughout the liberated areas," he said, using an Arabic abbreviation for the IS group.

"All told, the SDF overwhelmed ISIL forces around Shadadi and isolated the city in just six days, which was much faster than the SDF had estimated for the operation."

Garver said US commandos had played a "pretty significant role" in winning the fight.

Al-Shadadi was strategically important for the IS group, who used it as a logistics hub and a waypoint for rapid movement between Syria and Iraq.

"The loss of Shadadi increases the time, difficulty and risk to Daesh as it attempts to move between Syria and Iraq," Garver said.

"Our operations are reducing freedom of movement to Daesh and increasing the difficulty to their operations."

Pentagon officials have suggested Al-Shadadi's recapture marks an important milestone as local forces prepare for an assault on Raqa, the IS group's de facto capital in Syria.