Syrian rebels have cast doubt on claims that the head of the al-Qaeda-linked Nusra Front, Abu Mohammed al-Jolani, has been killed in western Syria.
State-run TV said he had been killed in the coastal province of Latakia, but provided no details.
A source in Latakia later told the BBC that Mr Jolani was believed to have left the area some time ago.
A rebel commander near Damascus told AP news agency said he believed Mr Jolani was "alive and well".
UK-based activist group the Syrian Observatory for Human Rights said that senior Nusra Front leaders contacted by activists had also denied Jolani had been killed.
A BBC source in Latakia said that contacts in the Nusra Front denied any knowledge that Mr Jolani had been on the front line on Friday.
The source confirmed that Jolani had visited the front about three weeks ago but said he had since left.
He added that rural areas of Latakia had come under intense shelling on Friday and that six people were killed and 10 were injured in the Al-Akrad mountain area.
The Nusra Front has emerged as one of the most powerful rebel groups since the uprising began in March 2011.
It first announced its existence in a video in January 2012 and has said it was behind many of the suicide bombings that have rocked the country.
The group is believed to have led numerous attacks against government targets, including the capture of a key airbase in the north.
In response to the bombing campaign the US designated the Nusra Front as a terrorist organisation.
Fighters from the Nusra Front were reported to be among some 20 rebels killed in an ambush by government forces near the capital Damascus on Friday.
The ambush happened in the Eastern Ghouta region, scene of August's poison gas attack that prompted a UN Security Council resolution calling for the destruction of Syria's chemical weapons arsenal.
State TV broadcast images showing bodies of men lying in an open area near a small river, along with scattered automatic rifles and hand grenades. A caption read: "Eastern Ghouta is a graveyard of terrorists''.
The Syrian government brands all the rebels fighting against it "terrorists".
"It was a highly accurate operation. `We will be moving from one victory to another," an army officer told state-run Al-Ikhbariya TV.
The Syrian Observatory for Human Rights said at least 20 fighters were killed in the ambush but gave no further details.
In another development, at least 20 people including children were reported killed in a car bomb blast in Syria, outside a mosque in a town in Damascus province.
The blast, in the town of Suq Wadi Barada, came just before the end of Friday prayers and brought down the mosque's entrances.
At least three children were among the dead and dozens more wounded, the Observatory said.
State media blamed opposition forces, saying the bomb exploded while it was being assembled. However, rebel leaders blamed government troops.