Millions of Shia Muslims are gathering at shrines and mosques for Ashura, which falls on the tenth day of the holy month of Muharram. The festival commemorates the slaying of Prophet Muhammad's grandson Hussein at the battle of Kerbala, now in southern Iraq, in AD 680.

Shias beat their heads and chests with chains and knives, and gash their heads with swords to show their grief and echo the suffering of Imam Hussein.

Ashura 2015
Blood pours down a Shi\'ite Muslim man\'s face after flagellating himself during a procession in Srinagar, Kashmir Danish Ismail/Reuters
Ashura 2015
An Afghan Shi\'ite Muslim man bleeds as he flagellates himself with chains during an Ashura procession in Kabul Omar Sobhani/Reuters

This year the festival is marked during a particularly turbulent time in the Middle East, which has seen an increase in sectarian violence alongside the spread of the Islamic Sate and other extremist Sunni groups, who believe Shia Muslims are apostates deserving death.