The chief of Syria's Al-Nusra Front, an Al-Qaeda affiliate, called Tuesday for an end to fighting between rebel groups and the jihadist Islamic State of Iraq and the Levant (ISIL).
The message came as the Syrian Observatory for Human Rights, a monitoring group, said at least 274 people had been killed in the clashes that erupted last Friday.
In an audio recording posted on Twitter, Abu Mohamed al-Jolani announced an initiative to end the fighting, including a "ceasefire" and the establishment of an independent Islamic committee to serve as mediator.
"This unfortunate situation pushed us to launch an initiative to solve the situation," Jolani said.
"It consists of forming a committee based on Islamic law and composed of the key brigades (and)... the establishment of a ceasefire," he said.
The initiative also calls for an exchange of prisoners and urges all fighters "to give priority to the fight against the regime."
In recent days, widespread fighting has broken out pitting coalitions of Islamist and moderate rebel forces against ISIL.
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The Observatory NGO said 129 fighters from moderate and Islamist rebel groups had been killed in the clashes, along with 99 ISIL members and 46 civilians.
The Nusra Front, which is Al-Qaeda's official affiliate in Syria, was established in mid-2011 when ISIL's Iraqi precursor dispatched members to the conflict.
In April 2013, ISIL chief Abu Bakr al-Baghdadi announced his Iraqi group and Al-Nusra would merge, but Jolani rejected the merger and pledged allegiance directly to Al-Qaeda chief Ayman al-Zawahiri.
Zawahiri also rejected the merger, urging ISIL to contain its operations to Iraq and naming Nusra Al-Qaeda's official affiliate in Syria.
Jolani's message on Tuesday blamed ISIL for the outbreak of rebel-jihadist fighting.
"The flawed policy of the Islamic State in the field had a key role in fuelling the conflict," he said.
He said the fighting "risks costing us dearly on the ground if it continues, particularly on the Aleppo front, for those under siege in Homs, and for the residents of Damascus and Ghouta (in Damascus province)."
"If the fighting is not resolved, the jihad formed by the muhajireen (foreign fighters) and the ansar (local fighters) risks losing lots of ground," he warned.
"The regime will gain new life when it was close to collapse and the West and the rafidain (Shiites and Alawites) will find a great space," he added.