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.
Israel pounded Lebanon with more than 120 air strikes on Tuesday in one of the heaviest days of bombing in weeks, Lebanese security sources said, as Israeli Prime Minister Benjamin Netanyahu said his military was deepening its operations in the country.
Syria's transitional leadership has located remnants of former President Bashar al-Assad's clandestine chemical weapons programme, including raw materials and munitions similar to those used to carry out deadly gas attacks during the country's long-running civil war.
US President Donald Trump, who turns 80 next month, said "everything checked out perfectly" after having his physical on Tuesday at Walter Reed National Military Medical ​Center, following a year of public attention on apparently minor health issues.
US Secretary of State Marco Rubio said on Tuesday negotiating a deal with Iran could "take a few days," quashing hopes for an imminent end to the conflict a day after US forces conducted what Washington called defensive strikes in southern Iran.