A suicide assault on two security service bases in Syria's third city of Homs killed dozens of people, including a top intelligence chief, on Saturday, overshadowing peace talks in Geneva.
Syria's former Al-Qaeda affiliate Fateh al-Sham Front claimed the spectacular attack which targeted and killed General Hassan Daabul, a close confidant of President Bashar al-Assad.
The Syrian Observatory for Human Rights said 42 people were killed when the bombers targeted the headquarters of state security and military intelligence in the heavily guarded Ghouta and Mahatta neighbourhoods.
Provincial governor Talal Barazi said 30 people were killed and 24 wounded.
State television confirmed Daabul's death, saying that the general had been specifically targeted by one of the suicide bombers.
The bombers engaged in prolonged gun battles with intelligence officers before blowing themselves up.
Observatory chief Rami Abdel Rahman said they lasted two hours.
Fateh al-Sham said five of its militants took part in the assault. State television and the Observatory spoke of six bombers.
Homs has been under the full control of the government since May 2014 when rebels withdrew from the centre under a UN-brokered truce deal.
But it has seen repeated bombings since then. Twin attacks killed 64 people early last year.
Like its jihadist rival, the Islamic State group, Fateh al-Sham is not party to a ceasefire between government forces and rebel groups taking part in the Geneva talks.
Despite renouncing links with Al-Qaeda last year, it remains blacklisted as a "terrorist" group by the United Nations and Western governments.
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The group overran almost all of the northwestern province of Idlib in 2015 in alliance with Islamist rebels.
But relations have since frayed as its allies have joined peace negotiations with the government, first in Kazakhstan earlier this year and then in Geneva.
Fateh al-Sham has meanwhile been targeted by intensifying air strikes, not just by the government but also by its ally Russia and by the US-led coalition fighting IS.
Scores of its fighters have been killed since the start of the year.
The tensions have triggered deadly clashes between the jihadists and their erstwhile allies in Ahrar al-Sham -- the largest Islamist rebel faction.
- Peace talks -
Saturday's attack comes as the UN is struggling to get the new round of peace talks in Geneva off the ground aimed at ending the six-year civil war which has killed more than 310,000 people.
UN envoy Staffan de Mistura said that despite government and rebel delegations being present for the talks there had been little discussion of substance between the rival parties.
"We discussed issues relating to the format of the talks exclusively," said Syrian regime delegation chief Bashar al-Jaafari after meeting de Mistura on Friday.
The Homs attack came after IS claimed a Friday suicide bombing that the Observatory said killed 83 people including 45 civilians outside the northern town of Al-Bab, which Turkish-backed rebels said this week they had taken from the jihadists.
The Observatory said that a car bomb targeted twin command posts at a rebel base in Susian, about eight kilometres (five miles) from Al-Bab, which was one of IS's last remaining strongholds in Aleppo province.
Separately, two Turkish soldiers were killed in a suicide attack in Al-Bab on Friday as they were carrying out road checks.