Syrian President Bashar al-Assad vowed to "cleanse" his country of extremism on Friday, a day after a suicide bomber killed more than 45 people in a mosque including a key pro-regime Sunni cleric.
The attack was also condemned by the opposition, who raised the possibility that the regime was behind the deadly blast at the Iman Mosque in Damascus on Thursday night.
State news agency SANA said that 49 people had been killed, including Mohamed Saeed al-Bouti, the most prominent Sunni Muslim cleric to back Assad's Alawite minority-dominated regime against a Sunni-led uprising.
The Syrian Observatory for Human Rights put the death toll at 46, saying that around 15 of the wounded were in critical condition and the toll was likely to rise.
The attack came as heavy fighting raged across Syria and as EU foreign ministers met in Dublin to discuss controversial calls by Britain and France for an easing of the bloc's arms embargo to allow weapons deliveries to the rebels.
Stepping into two days of talks between EU foreign ministers, Germany's Guido Westerwelle said Berlin remained "very reluctant" about weapons deliveries.
Austria's Michael Spindelegger too voiced strong opposition, adding that it was shared by the Czech Republic, Finland, Luxembourg and Sweden.
"We don't need more weapons in Syria," he said. "We need a political solution."
In echoes of sectarian violence in Iraq, state media said Thursday's attack was carried out by a suicide bomber who blew himself up after entering the central Damascus mosque, where Bouti was addressing religious students.
His grandson was among the dead.
Bouti's death is a blow to Assad's regime, 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 more than 70,000 people, according to UN figures, and caused more than one million to flee abroad.
Pro-government television aired gruesome footage from inside the mosque, where dozens of corpses were strewn on the carpeted floor in pools of blood.
In a statement issued by the presidency, Assad condemned the attack and mourned Bouti's death, vowing to eradicate "extremism and ignorance" in Syria.
"I swear to the Syrian people that your blood, and that of your grandson and all the martyrs of the homeland, will not be spilled in vain, because we will be faithful to your ideas by destroying their extremism and ignorance until we have cleansed the country," he said.
Bouti's funeral is scheduled for Saturday at Damascus's famous Umayyad Mosque, with authorities declaring a day of national mourning in his honour.
Ahmed Moaz al-Khatib, the head of the umbrella opposition National Coalition, condemned the cleric's killing as a "crime" and suggested the regime could have been behind it.
The United Nations Security Council set aside differences over the Syria conflict to agree a rare joint statement condemning the attack, which was also denounced by Iran, a staunch ally of the Assad regime.
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 much of the opposition, and frequently lashed out against the rebels while encouraging Syrians to join the army to fight against them.
Despite his prominence, a security official in Damascus said Bouti had refused to use bodyguards or an armoured car and was opposed to searches of people entering the mosque.
Fighting continued throughout the country on Friday, with the Observatory reporting clashes and regime shelling in southern neighbourhoods of the capital and heavy fighting in southern Daraa province.
A Syrian security official told AFP on Thursday that some 2,500 trained and equipped rebels had entered Daraa province in recent weeks, following reports that American instructors were training rebels in neighbouring Jordan.
A preliminary Observatory toll said at least 38 people had been killed nationwide on Friday, with the death toll for Thursday at 236.