Turkey's Prime Minister has singled out the Islamic State (IS) group as the prime suspect for Saturday's twin bombing in Ankara.

Ahmet Davutoglu had earlier said that three other banned organisations could be responsible.

And pro-Kurdish Peoples' Democratic Party leader Selahattin Demirtas says the government has "blood on its hands".

So who is to blame? Diplomatic correspondent Caroline Hawley answers key questions about the case.

Video produced by Howard Johnson