Derna, Libya isn’t a huge city, but its importance among Islamist factions in the nation is huge, as for decades through the Gadhafi regime it was the headquarters for most of the Islamist resistance to his rule. Since then, it has also been the home base of the local ISIS faction, and al-Qaeda-linked Mujahadeen Shura Council.

After nearly a solid week of street battles in Derna, the Mujahadeen are claiming victory over ISIS, and claim to have chased them almost entirely out of the city, saying they control 90% of the city and are just mopping up the last of the ISIS snipers therein.

While ISIS controls enough of the nation’s central coast at this point that Derna wouldn’t be a decisive defeat, the significance of the city, as well as the fact it houses their headquarters, would make the loss quite damaging to their momentum.

The fighting between the two factions began last week when a Mujahadeen leader was gunned down in Derna, an attack the faction blamed on ISIS. They launched an offensive against them thereafter, and it quickly spread city-wide. ISIS forces continue to advance around the city of Sirte, and toward Misrata, which would be their new power base.