A Syrian monitoring group says heavy fighting between rival rebel factions in eastern Syria has killed more than 60 fighters and forced tens of thousands of people to flee their homes in the past few days.
The Britain-based Syrian Observatory for Human Rights says rebels from the al-Qaida breakaway group Islamic State of Iraq and the Levant (ISIL) and the Nusra Front have been fighting over control of territory they previously took from Syrian government forces.
The Observatory says clashes over the past four days have left 62 fighters dead and displaced civilians from the towns of Abreeha and al-Busarayah in the oil-producing province of Deir al-Zor.
The two rebel groups have clashed repeatedly over strategic positions in the desert province which borders Iraq.
Meanwhile in Homs, contacts are under way to implement an agreement to allow rebel fighters and civilians to leave the government-besieged Old City. On Friday, rebels agreed to surrender the area in exchange for safe passage to other opposition-held areas in the north of Homs province.
At least 150,000 people have died in the Syrian civil war, which began in March, 2011 as protests against President Bashar al-Assad.
On Sunday, Syria's Supreme Constitutional Court announced that Mr. Assad and two other candidates will compete in the country's June 3 presidential election.
The incumbent will face challenges from lawmakers Hassan bin Abdullah al-Nouri and Maher Abdul-Hafiz Hajjar.
The court says only three of the 24 applicants met the legal requirements to run in the vote, which is widely expected to be won by Mr. Assad.