A suicide bomb attack on a central Damascus mosque on Thursday killed 42 people, including Syria’s most prominent pro-regime Sunni cleric, and wounded dozens of others, the health ministry said, according to AFP.

The bomber blew himself up inside the Iman Mosque as the cleric, Mohamed al-Bouti, addressed religious students, in an attack that echoed sectarian violence in Iraq.

“The number of those martyred in the terrorist suicide attack in the Iman Mosque rises to 42 martyrs with 84 injured,” state television said, citing the health ministry.

Bouti, noted AFP, was the most senior pro-regime Sunni cleric in Syria whose weekly addresses at Friday prayers were frequently broadcast live on state television.

His death will be a blow to the regime of President Bashar al-Assad, which has been fighting an insurgency that flared when his forces launched a bloody crackdown on Arab Spring-inspired democracy protests that erupted in March 2011.

The relentless violence has killed tens of thousands of people and caused more than one million to flee their homes as refugees.

Pro-government television aired gruesome footage from inside the mosque, where dozens of corpses and body parts, including limbs and hands, were strewn on the carpeted floor among pools of blood.

Emergency workers collected the remains and carried them out in grey body bags.

Ahmed Moaz al-Khatib, the head of the umbrella opposition National Coalition, condemned the cleric’s killing as a “crime,” and suggested the regime itself could have been be behind it.

“We categorically condemn the assassination of the scholar Dr. Mohamed Saeed Ramadan al-Bouti,” Khatib told AFP.

“This is a crime, by any measure, that is completely rejected,” he said. “Whoever did this was a criminal… and we suspect it was the regime.”

Khatib, himself a cleric, said he had known Bouti, who was held in high esteem among Islamic theologians, but had disagreed with him over his vociferous support for Assad.

Born in 1929, Bouti was from a large Kurdish family and spent years studying Islam, including at Cairo’s al-Azhar University.

He was reviled by the opposition, and frequently lashed out against the rebels while encouraging Syrians to join the army to fight against them, reported AFP.

The regime is dominated by members of the minority Alawite sect and had relied in part on the cleric to bolster its claims to represent all Syrians, including Sunnis, from whom the opposition draws much of its support.

Thursday’s attack came as heavy fighting raged across Syria, and UN Secretary General Ban Ki-Moon said the United Nations would investigate whether chemical weapons have been used in the conflict.

On Wednesday, Britain, France and the United States called for a United Nations inquiry into accusations by the Syrian government and the opposition of chemical weapons attacks.

Both Syrian rebels and the Assad regime had claimed that chemical weapons were used in an attack on Tuesday on the cities of Aleppo and Damascus, in which 25 people were killed and dozens more injured. Each side was accusing the other of being responsible for the attack.

The chairman of the U.S. House Intelligence Committee, Rep. Mike Rogers, later said that there is a “high probability” that Syria used chemical weapons in the ongoing civil war.

“We need that final verification, but given everything we know over the last year and a half, I would come to the conclusion that they are either positioned for use, and ready to do that, or in fact have been used,” he told CNN.

An Israeli source was more firm on the matter, confirming that chemical weapons were used in attacks on the cities of Aleppo and Damascus.

On Wednesday, Minister of Intelligence and Strategic Affairs Yuval Steinitz said in an interview that it is “apparently clear” that either Syrian rebels or the Damascus regime have used chemical weapons in the country’s two-year civil war.

“This is very concerning for us and we must deal with it urgently,” said Steinitz.

U.S. President Barack Obama, however, was more careful when asked about the situation during his news conference with Prime Minister Binyamin Netanyahu.

Obama indicated that not all the facts on what happened in Syria on Tuesday were clear, saying, “With respect to chemical weapons, we intend to investigate thoroughly exactly what happened. Obviously in Syria right now you’ve got a war zone, you have information that’s filtered out, but we have to make sure that we know exactly what happened, what was the nature of the incident, what can we documented, what can be proved.”