The Syrian government vowed retribution for synchronized attacks on Saturday in Homs City that left 42 security personnel dead and reportedly involved up to six suicide bombers.
"The terrorist attacks that hit the city of Homs today were a message from the sponsors of terrorism to Geneva," said Bashar al-Jaafari, the government's top envoy to the peace talks held in Switzerland.
Saturday marks the third day of the negotiations that resumed after a break of 10 months.
"We tell everyone that this message has been received and that we won't let this crime pass without retribution," al-Jaafari told reporters before heading to a meeting with UN mediator Staffan de Mistura.
Forty-two security personnel were killed in attacks targeting government security facilities in Homs, the Syrian Observatory for Human Rights said.
Among the dead was the chief of a branch of the military intelligence service, the monitoring group said. State media identified him as Major General Hassan Daboul.
State news agency SANA reported that the attacks, carried out by six suicide bombers, killed 50 people, both military personnel and civilians.
The attackers targeted the offices of military intelligence and state security services in the neighbourhoods of al-Ghouta and al-Mahata in the central city.
The al-Qaeda-linked Jabhat Fatah al-Sham claimed responsibility for the attacks.
The militant group, previously known as al-Nusra Front, said in an online statement that five suicide bombers had simultaneously attacked the two security buildings and blew themselves up there.
The statement could not be verified by dpa.
Jabhat Fatah al-Sham and Daesh extremist militia are excluded from a Russian-Turkish brokered ceasefire that went into effect in Syria in late December.
In recent months, both groups have taken credit for deadly attacks in different parts of Syria.
Daesh claimed responsibility for a car bombing in the northern Syrian city of al-Bab on Friday that killed 77 people.
The fatalities in the suicide attack outside a Syrian rebel command centre in Suesian north of al-Bab included 41 civilians, the Observatory reported Saturday.
The bombing came a day after Turkish-backed Syrian rebels seized al-Bab from Daesh.
Operations to take al-Bab from Islamic State began in November and suffered several setbacks as the militants used landmines, explosives-packed cars and tunnel networks, according to Turkish sources. Daesh has now fully retreated from the city.
Al-Bab is being closely watched as Turkey weighs its next steps inside Syria. Ankara sent forces over the border in August last year. The Syrian government deems the presence an occupation.
Turkey says it killed hundreds of Islamic State fighters, though the numbers cannot be verified.
Meanwhile, the Observatory said government jets have carried out strikes on Homs City, the area of Douma, located on the outskirts of Damascus, as well as the western outskirts of Aleppo.
The deadliest airstrikes were in Douma, killing nine people, the observatory said.
On Wednesday, de Mistura said that Russia has asked the Syrian government to halt military aerial operations during the peace talks.
By Khalil Hamlo and Ramadan al-Fatash
