Negotiations off to rocky start after opposition threatens to skip opening ceremony over disagreements.
The Syrian military intelligence chief is among at least 32 people killed in a series of suicide attacks on military installations in the government-held western city of Homs.
The death of General Hassan Daabul, a close confidant of President Bashar al-Assad, in Saturday’s bombings was reported by the Syrian state television.
A witness was quoted as saying a suicide bomber actually made it into Daabul’s office and detonated the explosives.
Brigadier Ibrahim Darwish, head of the State Security Branch, was also critically wounded, state-affiliated Al Ikhbariya TV reported.
The Britain-based Syrian Observatory for Human Rights (SOHR) said air raids by government forces killed another 13 people across the country, including at least three in al-Waer, a rebel enclave of Homs.
Speaking to Al Jazeera in Geneva, Issam al-Reis, spokesperson for the Southern Front branch of the Free Syrian Army (FSA), accused the Assad government of staging the attacks to influence the Geneva talks.
“During the last Geneva talks an explosion happened in the government area of Sayyda Zeinab, but now we’re talking about military and security branches, which is a military zone inside the [Homs] Green Zone. No one is allowed to enter these areas – not even close,” he said.
“So, obviously, this order is coming from the same branch to make these explosions because the pressure the regime is getting from Russia to be in the ceasefire may have pushed the regime to find an excuse to launch an attack.”
Talal Barzani, the Homs provincial governor, said there were three blasts in total, killing 32 people and wounding more than 20 others.
The SOHR, which put the Homs toll at 42, said loud explosions and gunfire were heard following the assault.
“There were at least six attackers and several of them blew themselves up near the headquarters of state security and military intelligence,” Rami Abdel Rahman, SOHR’s director, told AFP news agency.
Bombers engaged in prolonged gun battles with intelligence officers before detonating their explosive vests.
Steffan de Mistura, the UN envoy for Syria, said he suspected “spoilers” were trying to derail the negotiations.
“I’m expecting during these talks, unfortunately, spoilers,” he said.
“Every time we had talks or a negotiation, there was always someone who was trying to spoil it – we were expecting that.”
Homs has been under the full control of the government since May 2014 when rebels withdrew from the city centre under a UN-brokered truce.
But it has seen repeated bombings since then: a double bombing killed 64 people early last year.
“Today, the Syrian government responded to a brutal terrorist attack in Homs by indiscriminately bombing innocent men and women in besieged al-Waer,” Mazen Kewara, of the Syrian American Medical Society, told Al Jazeera on the sidelines of the conference.
“Targeting innocent women and children in retribution for terrorist attacks for which they bear no responsibility is barbaric and a gross violation of international humanitarian law. If these indiscriminate attacks don’t stop, they will delegitimise the peace talks in the eyes of ordinary Syrians.”
Kewara’s views were echoed by Mutasem Alsyofi of The Day After, a collection of civil society activists, in an interview with Al Jazeera in Geneva.
“Parties with blood on their hands cannot be trusted to monitor their own war crimes,” he said.
“We want the Geneva process to succeed, but success starts by upholding international law and stopping the violence. As long as barrel bombs and chemical weapons are met with impunity, prospects for peace will remain dim.”
Saturday’s attacks hit the heavily guarded Ghouta and Mahatta neighbourhoods, prompting security forces to lock down Homs’ city centre.
Al Jazeera’s Andrew Simmons, reporting from Gaziantep on the Turkey-Syria border, said it was unclear how the assailants could have pulled off Saturday’s attacks in Homs.
“Both areas are heavily guarded by the state police and the military, so it was a really big and organised twin attack,” he said.
Bashar al-Jaafari, who leads the Syrian government delegation to the talks in Geneva, said Saturday’s attacks, would not go unanswered.
He said they “were a message to Geneva from the sponsors of terrorism. The message has been delivered”.
An anti-government alliance known as Tahrir al-Sham is believed to have carried out the Homs attacks.
Since it was formed, Tahrir al-Sham has fought other rebel groups, including some that fight under the banner of the FSA, as well as a faction linked to Islamic State of Iraq and the Levant (ISIL) group, in northwest Syria.
Like its rival ISIL, also known as ISIS, Jabhat Fateh al-Sham is not party to a ceasefire between government forces and opposition groups taking part in the Geneva talks.