Car bomb in Syria kills five
The Britain-based Syrian Observatory for Human Rights said the bombing occurred in the troubled eastern province of Deir el-Zour near the offices of the al Qaida-linked Nusra Front and another group, Ahrar al-Sham.
The Observatory, which relies on a network of activists on the ground, says an Ahrar al-Sham commander in the area and an Islamic judge affiliated with the Nusra Front were among those killed in the blast.
There was no claim of responsibility for the bombing but blame is likely to fall on the rival faction known as the Islamic State of Iraq and the Levant (Isis), which is behind the insurgency in northern Iraq.
The Nusra Front and Ahrar al-Sham have been fighting against against Isis in Syria's oil-rich province since April.
The rebel infighting has killed more than 640 people on both sides and uprooted at least 130,000 civilians from their homes.
The violence also has weakened the opposition's ability to fight president Bashar Assad's forces, which over the past year regained much of the territory in and around Syria's major cities, including the capital Damascus.
In a separate attack in Deir el-Zour, an Isis member detonated an explosive belt outside the home of a local rebel commander in the village of Huwayej, wounding him and killing two of his sons, the Observatory said.
The Observatory also reported heavy clashes between Isis and its rivals on the edge of the town of Basira in eastern Syria, as the jihadi fighters try to advance toward the nearby village of Shuheil.