BEIRUT (AP) — A U.S.-backed Syrian force says it has captured a northwestern neighborhood of the Islamic State group's de-facto capital of Raqqa after two days of fighting.

The Kurdish-led Syrian Democratic Forces says its fighters captured on Sunday the neighborhood of Romaniah after two days of fighting that left 12 IS gunmen dead, including a commander known as Abu Khattab al-Tunsi.

The Britain-based Syrian Observatory for Human Rights said SDF fighters now control Romaniah and the eastern neighborhood of Mashlab. The fighters have also entered Raqqa's western neighborhood of Sabahiya.

SDF fighters began their offensive on Raqqa city on June 6 under the cover of airstrikes by the U.S.-led coalition.

The battle is likely to be long and difficult as the extremist group is expected to fiercely defend its self-declared capital.