(CNN) -- ISIS has apparently taken a heavy hit over the past several days. The bodies of at least 70 fighters for the terror group have been dropped off over four days at a hospital in the Syrian town of Tal Abyad, a Syrian opposition group told CNN. Tal Abyad is on the Turkish border and about 80 kilometers (50 miles) from Raqqa.
The Islamic State in Iraq and Syria took control of Raqqa last year. ISIS uses the once-liberal city as a kind of headquarters where it applies its hardline interpretation of Islamic law, terrorizing the population.
Kurdish and Iraqi forces have been battling ISIS on the ground. With the help of airstrikes from an international coalition led by the United States, the foot soldiers are now focused on pushing ISIS back from its relentless attempt to take Kobani, a Kurdish town on the Syrian-Turkish border.
It's unclear who dropped the bodies of the ISIS fighters off at the hospital, but sources who work in local medicine confirmed their delivery to the Syrian Observatory for Human Rights, a group that promotes ending the longstanding regime of Syrian President Bashar al-Assad. The group is based in London and first formed when violence broke out in Syria in 2011, much of it geared toward ousting al-Assad.
Kobani now is the scene of an unrelenting battle. On Sunday, the brief moments of calm were punctuated by sounds of firing from both sides. ISIS has shelled the city at least 16 times, sources say, while coalition planes fly low overhead.
The strategy against ISIS is working, said U.S. Central Command Gen. Lloyd Austin on Friday. He also said that Kobani could fall.
U.S. warplanes struck only twice Friday and Saturday in the city, Central Command said, both times targeting ISIS fighting positions. That's far fewer strikes than days before. U.S. jets flew at least 14 missions near Kobani on Thursday and Friday, the military reported.
It will take "strategic patience" to beat ISIS, Austin said.
The U.S. has generally downplayed the importance of Kobani as a key city in the battle against the militants.
However, if ISIS takes Kobani, that would mean it would control land between Raqqa and Turkey -- about 100 kilometers (60 miles).
CNN's Raja Razek contributed to this report.