Gunmen and suicide bombers have attacked security bases in Homs, western Syria, killing at least 32.
State TV said the local head of military intelligence was among the dead and some reports say more than 40 died. Jihadist group Tahrir al-Sham said it carried out the attacks.
Homs has been under government control since December 2015 when rebels left under a ceasefire deal.
Syria's government said the attacks would not go unanswered.
Its UN Ambassador Bashar al-Jaafari, who leads the government delegation at peace talks in Geneva, said they were a message to the talks from "the sponsors of terrorism".
He demanded that all opposition groups present denounce the violence, saying direct talks could only be held with a unified opposition.
Syria's main opposition camp later said that it condemned "all terrorist operations committed by terrorist groups".
UN special envoy Staffan de Mistura said he hoped the attacks would not affect the talks.
"It was tragic, terrible, and that's why, you know, I'm expecting during these talks unfortunately spoilers," he said.
"Every time we had talk, or negotiation, there was always someone who tried to spoil it. We were expecting that."
Tahrir al Sham which is led by al-Qaeda's former affiliate in Syria, is part of neither the current ceasefire nor the peace talks.
The Syrian Observatory for Human Rights, a monitoring group, said attackers targeted the headquarters of military security in the city and also a branch of state security.
The attacks took place in the heavily guarded Ghouta and Mahatta districts.
State TV said provincial army intelligence chief General Hassan Daabul, a close associate of President Bashar al-Assad, was among the dead.
After the attacks, government planes carried out air strikes on the last opposition enclave in Homs, though rebels there are not connected to Tahrir al-Sham.
The jihadists said five of their fighters had taken part in the assault.
The group was formed when Jabhat Fateh al-Sham, known as the Nusra Front until it broke off formal ties with al-Qaeda last July, merged with four smaller Syrian factions.
Earlier this month it announced that its leader was Hashim al-Sheikh, who previously served as head of the powerful Islamist rebel group, Ahrar al-Sham.