Syria's Islamist Ahrar al-Sham rebel brigade named new chiefs on Wednesday after a devastating blast killed nearly 50 members of its leadership in a northwestern province largely under rebel control.
The blast in Idlib province on Tuesday evening killed the key rebel group's leader Hassan Abboud, known by the name Abu Abdullah al-Hamawi, along with 46 other top members.
The attack targeted a meeting of around 50 military and religious leaders in the basement of a house at Ram Hamdan, northeast of Idlib city.
The initial death toll in the attack was 28, but it rose to 47 on Wednesday morning, the Syrian Observatory for Human Rights said.
On Wednesday morning, in a video posted on YouTube, Ahrar al-Sham announced that Hashem al-Sheikh, known as Abu Jaber, would replace Abboud as head of the group, with Abu Saleh Tahhan as military commander.
"A group of the best chiefs of Ahrar al-Sham have been martyred. But Ahrar al-Sham is more determined than ever to continue on the path to liberating our country from dictators," the video statement said.
Ahrar al-Sham is a key component in the Islamic Front rebel coalition, which has been battling both President Bashar al-Assad's regime and jihadists of the Islamic State group.
No group has claimed the attack on Ahrar al-Sham's leadership and the rebel brigade has not officially pointed the finger at any organisation.
It was also unclear what caused the blast, whether a planted bomb, an attacker wearing explosives or even an air strike.
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But the Observatory said it believed the blast had been caused by a bomb planted in the entrance to an underground bunker where the leadership was meeting.
The blast blocked the only route out of the bunker and many of those killed died from asphyxiation, the Britain-based group's director Rami Abdel Rahman told AFP.
All of Idlib province is under rebel control apart from Idlib city. IS fighters were pushed out of the province earlier this year.
Elsewhere in Syria, the Observatory said the toll in two regime air raids on the town of Douma in Damascus province on Tuesday rose to 25, including 10 children.
In Quneitra province meanwhile, rebel forces continued to advance, with the Observatory saying opposition forces were now in control of 70 percent of the region.
Last week, rebel forces seized the Syrian side of the province's crossing with the Israeli-occupied portion of the Golan Heights plateau.
In eastern Deir Ezzor province, the Observatory said Syrian war planes continued aerial raids against the provincial capital.
Three jihadists from the Islamic State group were killed in the raids on Deir Ezzor city, along with nine civilians, three of them children, the group said.
Three other civilians were killed in an air raid elsewhere in the province, the Observatory added.
More than 180,000 people have been killed in Syria since an uprising against Assad's rule erupted in March 2011.