A series of suicide attacks on military installations in Syria's government-held city of Homs are reported to have killed 32 people, including the army's intelligence chief - a close confidant of President Bashar al-Assad.

Syrian state television said the army's intelligence chief General Hassan Daabul died and it paid tribute to the "martyrs" in Saturday's bombings.

The UK-based Syrian Observatory for Human Rights (SOHR) said loud explosions and gunfire were heard following the assault in the western Syrian city.

"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.

Talal Barzani, the governor of Homs province, 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 air raids by government forces killed another 13 people across the country, including at least three in al-Waer, a rebel enclave of Homs.

Geneva talks

The violence comes as officials from the Assad government and the opposition meet for a fourth round in Switzerland to end Syria's six-year-old civil war that has killed hundreds of thousands of people.

"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."

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Kewara's views were echoed by Mutasem Alsyofi of The Day After, a collection of civil society activists, in an interview to 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."

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."

'Big and organised' attack

Saturday's attacks in Homs hit the heavily guarded Ghouta and Mahatta neighbourhoods, prompting security forces to lock down the city centre.

A witness was quoted as saying a suicide bomber actually made it into Daabul's office and detonated his vest.

Brigadier Ibrahim Darwish, head of the State Security Branch, was also critically wounded, state-affiliated al-Ikhbariya TV reported.

Al Jazeera's Andrew Simmons, reporting from Gaziantep on the Turkey-Syria border, said it was unclear how the assailants could have pulled off such an assault.

"Both areas are heavily guarded by the state police and also military so it was a really big and organised twin attack," said Simmons.

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".

A rebel alliance known as Tahrir al-Sham is believed to have carried out the attack.

It was formed earlier this year from several groups including Jabhat Fateh al-Sham, formerly known as al-Nusra Front, which was al-Qaeda's Syrian branch until it broke formal allegiance in 2016.

Since it was formed, Tahrir al-Sham has fought other rebel groups, including some that fight under the banner of the Free Syrian Army, as well as a faction linked to Islamic State of Iraq and the Levant (ISIL) group, in northwest Syria.

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 the city has seen repeated bombings since then. Double bombings killed 64 people early last year.

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.