Authorities in Syria have made a number of arrests after an attack on a church in which the health ministry said that 25 people were killed and 63 injured.
The shooting and suicide bombing happened at the Mar Elias Church in the Dwelaa district of the Syrian capital Damascus.
President Ahmed al-Sharaa vowed that those involved in the "heinous" attack, blamed on the Islamic State group, would face justice.
The Islamist authorities who took power after ousting longtime president Bashar al-Assad in December said the attacker was affiliated with IS, which has not yet claimed that it carried out the assault.
The interior ministry reported the arrest of "a number of criminals involved in the attack" as well as the seizure of explosive devices and a booby-trapped motorbike during a security operation near Damascus "against cells affiliated with the Daesh (IS) terrorist group".
The announcement came hours after President Sharaa vowed that authorities would "work night and day, mobilising all our specialised security agencies, to capture all those who participated in and planned this heinous crime and bring them to justice".
The attack follows incidents of sectarian violence in recent months, with security one of the greatest challenges for the new authorities.
The assault "reminds us of the importance of solidarity, and unity of the government and the people in facing all that threatens our nation's security and stability", Mr Sharaa said.
The attack was the first suicide bombing in a church in Syria since the country's civil war erupted in 2011, according to the Syrian Observatory for Human Rights monitoring group.
It was also the first assault of its kind in the Syrian capital since the ousting of Mr Assad.
During a visit to the church, Greek Orthodox Patriarch of Antioch John X said that a funeral service for some of the victims would be held tomorrow.
He told those gathered that "what happened is painful, but do not be afraid".
Since the new authorities took power, the international community has repeatedly urged them to protect minorities and ensure their participation in Syria's transition, particularly after the recent violence.
The top cleric of the country's Sunni Muslim majority, Grand Mufti Osama al-Rifai, condemned acts of violence and terrorism.
"We express our complete rejection of targeting places of worship and terrorising believers," he said in a statement.
There has been widespread condemnation of the attack.
Turkish President Recep Tayyip Erdogan said that his country would not allow extremists to drag Syria back into chaos and instability, vowing that would "continue to support the Syrian government's fight against terrorism".
Turkey, which is close to the new authorities, has repeatedly offered its operational and military support to fight IS and other militant threats.
French President Emmanuel Macron also denounced the "horrible" attack, while the European Union said it "stands in solidarity" with Syria in combating ethnic and religious violence.
"It is a grave reminder of the need to intensify efforts against the terrorist threat and to ensure the enduring defeat of Daesh and other terrorist organisations," EU foreign policy spokesperson Anouar El Anouni said, using the other name for IS.
Greece's Prime Minister Kyriakos Mitsotakis expressed anger after the attack on the Greek Orthodox Church, calling on the authorities "to take concrete measures to protect all ethnic and religious minorities".
United Nations Humanitarian Coordinator for Syria Adam Abdelmoula urged officials to take "all necessary steps to ensure the protection of civilians", saying there was "no room for violence and extremism".
The country's Christian community has shrunk from around one million before the civil war to fewer than 300,000 due to waves of displacement and emigration.
IS seized large swathes of Syrian and Iraqi territory in the early years of the conflict, declaring a cross-border "caliphate" in 2014.
The jihadists were territorially defeated in Syria 2019 but have maintained a presence, particularly in the country's vast desert.
