Eight people were killed in an explosion at a mosque of the Alawite minority sect in the Syrian city of Homs on Friday.
Syrian state news agency SANA cited health ministry official Najib al-Naasan as saying 18 others were wounded and that the figures were not final, indicating they could rise.
Homs city's press office said an explosive device had detonated inside the Imam Ali bin Abi Talib mosque and that security forces had cordoned off the area.
Local official Issam Naameh told Reuters the blast took place during Friday noon prayers, typically the busiest time for mosques.
There was no immediate claim of responsibility for the attack. Syria's foreign ministry condemned the blast as a "terrorist crime".
Syria has been rocked by several episodes of sectarian violence since longtime leader Bashar al-Assad, an Alawite, was ousted by a rebel offensive last year.
Earlier this month, two American soldiers and a civilian interpreter were killed in central Syria by an attacker described by the authorities as a suspected member of the IS.
The US and Iran failed to reach an agreement to end their war despite marathon talks that concluded on Sunday in the Pakistani capital Islamabad, jeopardising a fragile ceasefire.
Russia and Ukraine accused each other on Sunday of breaching the 32-hour ceasefire in their four-year war, reporting more than a thousand drone and shelling attacks just hours after the truce began on Saturday to mark Orthodox Easter.
At least 30 people were killed on Saturday in a stampede at the Laferriere Citadel in the northern countryside of Haiti, authorities said, warning that the death toll could rise.
A cyclone battered New Zealand's North Island on Sunday, cutting power to thousands of residents and forcing hundreds to evacuate, as officials warned conditions would worsen through the day.
Negotiations between the United States and Iran appeared to have concluded for now, Iran's government has announced early on Sunday, after a series of talks in Pakistan to end the six-week war between Washington and Tehran.