A suicide attack killed at least 30 people at a Shia Muslim mosque in Kabul, Afghanistan, on Monday.
Many more were wounded by the blast that was timed as worshippers gathered for prayer at the Baqir ul Olum mosque. Islamic State has claimed the attack – the latest on Afghanistan's Shia community by the Sunni militant group.
The service at lunchtime (0800 GMT) on Monday was to commemorate the death of Imam Hussein, the Prophet Muhammad's grandson and Shia martyr. Officials said the attack was a deliberate attempt to stoke sectarian tensions.
Bloody sectarian rivalry between Sunni and Shia Muslims has been relatively rare in Afghanistan, a majority Sunni country, but the attack underlines the deadly new dimension that growing ethnic tension could bring to its decades-long conflict.
Already there had been two major recent attacks on Shia targets in Kabul, both claimed by Islamic State.
One was on a demonstration by the mainly Shia Hazara community in July which killed more than 80 people, in the deadliest attack on civilians since 2001.
Last month, 18 people were killed when a gunman in police uniform opened fire on worshippers gathered at a shrine in Kabul for Ashura, one of the holiest occasions in the Shia calendar.
At least 14 people were also killed in an attack on a Shia mosque in northern Balkh province, for which no group has so far claimed responsibility.
Any resurgence of sectarian or ethnic violence could threaten the fragile stability of the government headed by President Ashraf Ghani, who described the mosque blast as an attempt "to sow seeds of discord".
Government Chief Executive Abdullah Abdullah said Afghanistan should not fall victim to "enemy plots that divide us by titles".
He wrote on Twitter: "This attack targeted innocent civilians - including children - in a holy place. It is a war crime & an act against Islam & humanity."
Thousands of civilians have been killed in Afghanistan in the 15 years since the Taliban government was brought down in the US-led campaign of 2001.
In July, the UN Assistance Mission in Afghanistan reported that 1,601 civilians had been killed in the first half of the year alone, a record since it began collating figures in 2009.
Additional reporting by Reuters.
