The Islamic State (IS) extremist group has claimed responsibility for an attack on a shrine in the Afghan capital, Kabul, that killed 18 people, mostly Shia mourners.

IS's affiliate in Afghanistan and Pakistan -- known as Khorasan Province -- claimed the attack in an online statement issued on October 12.

Interior Ministry spokesman Sediq Sediqqi said 62 people, including 12 police, were wounded in the attack on the Karte Sakhi shrine, one of the largest in Kabul.

He said that, contrary to earlier reports of three gunmen, only one gunman, who was later gunned down by security forces, attacked the shrine.

In a statement issued on October 12, the United Nations said the "attack deliberately targeting a large group of civilians exercising their right to freely manifest their religion in worship, observance, and practice is an atrocity."

In a statement issued on October 11, Afghan President Ashraf Ghani offered his condolences to the victims and condemned the attack as a "clear sign of a crime against humanity."

Afghan security forces at the scene had evacuated the shrine, where Shia mourners had gathered nearby to celebrate the festival of Ashura, one of the holiest on the Shia calendar.

Ashura commemorates the death of Imam Hussein, grandson of the Prophet Muhammad, who was killed in 680 and whose death laid the foundation for the Shia faith.

For Shia Muslims around the world, Ashura is a symbol of the struggle against oppression.

The mourning for the festival reaches its peak on October 12.

In July, an attack claimed by Islamic State (IS) extremists killed 84 people, many of them Shia from the ethnic minority Hazara group.

In 2011, 54 people were killed when a suicide bomber attacked another Kabul shrine where hundreds of people had gathered. A Shia mosque in the northern city of Mazar-e-Sharif was also hit on the same day, leaving four dead.

Kabul police had warned Shia-- mostly ethnic Hazara -- against large gatherings as attacks were expected.

By RadioFreeEurope/RadioLiberty?