A gunman opened fire and detonated an explosive belt at a packed church service in the Syrian capital Sunday, killing at least 22 people in what officials said was the first attack of its kind in Damascus since Islamist forces ousted longtime President Bashar al-Assad in December.

Authorities blamed the Islamic State group for the assault, which struck the Saint Elias Orthodox Church in the Dwelaa district. It was also the first suicide bombing inside a church since the start of Syria’s civil war in 2011, according to the Syrian Observatory for Human Rights.

The attack occurred during a crowded service, sending worshippers into panic. Blood stained the floors, and wooden pews were shattered across the church interior. Fallen religious icons lay among the debris as first responders evacuated the wounded.

"A suicide attacker affiliated with the Daesh (IS) terrorist group entered the Saint Elias church in the Dwelaa area... opened fire then blew himself up with an explosive belt," the interior ministry said in a statement.

State news agency SANA, citing the health ministry, said 22 people were killed and 63 injured.

Eyewitnesses described chaos and terror. Lawrence Maamari, who was inside the church at the time, told AFP that the attacker began shooting before detonating his explosives. People "tried to stop him before he blew himself up," he said.

Nearby shopkeeper Ziad Helou, 40, said he heard gunfire followed by an explosion.

"We saw fire in the church and the remains of wooden benches thrown all the way to the entrance," he said.

The international community swiftly condemned the attack.

The United Nations special envoy for Syria, Geir Pedersen, expressed “outrage at this heinous crime,” and called for a full investigation. U.S. special envoy Tom Barrack said Washington supported Syria "as it fights against those who are seeking to create instability and fear in their country and the broader region."

France’s foreign ministry reiterated its support for “a transition in Syria that allows Syrians, whatever their religion, to live in peace and security in a free, united, pluralistic, prosperous, stable and sovereign" country.

Turkey, which has close ties to Syria’s new authorities, voiced confidence that Syrians would remain united in “their fight against terrorist organisations that seek to sow chaos in the country.” Egypt’s Al-Azhar, Sunni Islam’s foremost institution, called the attack a “blatant assault on the right to life” and worship.

The Orthodox patriarchate in Damascus called on "the authorities to bear full responsibility for what has happened and is happening concerning the violation of the sanctity of churches, and to ensure the protection of all citizens."

Syria's Christian population has dwindled from around one million before the war to fewer than 300,000, following years of displacement and emigration.

The foreign ministry described the bombing as “a desperate attempt to undermine national coexistence and to destabilise the country.”

Interior Minister Anas Khattab said investigative teams had begun their work.

"These terrorist acts will not stop the efforts of the Syrian state in achieving civil peace," Khattab said in a statement.

Earlier this month, Khattab said IS had shifted “to studied attacks on strategic targets” and was attempting “to carry out attacks against the Christian and Shiite community” that authorities were trying to thwart.

Last month, IS claimed its first attack on Syria's new government forces since Assad's ouster. Officials said an IS cell preparing attacks near Damascus had been dismantled.

IS once controlled vast territory in Syria and Iraq, declaring a so-called caliphate in 2014. It was territorially defeated in 2019 but remains active in cells across the region.