KABUL (Reuters) - A suicide bomber attacked a Shi'ite Muslim shrine in central Kabul on Tuesday, where hundreds of people had gathered to celebrate the festival of Ashura, the head of Kabul's Criminal Investigation Department said.

Mohammad Zahir said there were casualties, possibly as many as 20, but there were no firm details yet.

The Shi'ite Muslim festival of Ashura marks the martyrdom of the Prophet Mohammad's grandson Hussein in the battle of Karbala in Iraq in the year 680.

(Reporting by Mirwais Harooni, writing by Emma Graham-Harrison, editing by Daniel Magnowski)