More than 22 people were killed and another nearly 60 were injured when an Islamic State suicide bomber attacked a church in the Syrian capital of Damascus, officials said.

Syrian Christians were struggling on Monday to understand why their community was targeted in a suicide attack and whether they can rely on the Islamist-led government's assurances of protection.

State media says a suicide bomber in Syria has detonated himself inside a church filled with people, killing at least nine.