A new round of fighting has erupted in eastern Syria, as al-Qaeda in Iraq (AQI) clashed with rival al-Qaeda faction Jabhat al-Nusra in the town of Khosham, in Deir Ezzor Province.

Fighting began Sunday night, according to rebel mouthpiece the Syrian Observatory for Human Rights, and continued into Monday. By the end, 17 Nusra and 28 AQI fighters were dead.

AQI tried to absorb the Nusra Front in early 2013, but since then what remains of Nusra’s fighters have openly challenged them with the rebel “war within a war” becoming more violent than the ongoing civil war is.

AQI has mostly gotten the better of these fights, and is carving out a territory of its own starting in Aleppo Province and moving deep into neighboring Iraq, where AQI is fighting for control of Fallujah and Mosul.