Opposition observatory said two weeks of fighting between an al-Qaeda-linked group and other opposition militants in Syria has killed more than 1,000 people.
The Britain-based observatory said today that the fighting in northern and eastern Syria killed 1,069.
The clashes pitting the al-Qaeda-linked Islamic State of Iraq and the Levant and other groups are the most serious among militant forces since the Syrian crisis which began in 2011.
The Observatory said that the dead included 130 civilians - including 21 who were executed by "Islamic State" members.
The United Nations human rights office said extremist Islamic groups are committing a soaring number of executions in the country's north that could amount to war crimes.