A suicide bomber blew himself up at a wrestling club in a Shia neighbourhood of the Afghan capital Kabul yesterday, and a second blast struck after the emergency services and journalists arrived at the scene.
At least 20 people were killed and 70 wounded, Nasrat Rahimi, an interior ministry spokesman said.
There was no immediate claim of responsibility. The attack occurred in Dasht-e-Barchi, home to many members of the mainly Shia Muslim Hazara ethnic minority which has been targeted in the past by Sunni militants of Islamic State.
Social media users who purportedly witnessed the attack said the bomber killed the guards at the club before blowing himself up inside.
He "detonated inside where a large number of athletes had gathered. There are a lot of dead and wounded", Mohammad Hanif said on Facebook.
A photo posted on Twitter purportedly showed several victims being loaded into the back of a police pick-up.
Last month, dozens of students preparing for a university entrance examination were killed at an educational centre in the area.
Kabul police spokesman Hashmat Stanekzai said the second explosion hit as police were helping victims and a number of journalists were at the site.
Last April, a suicide bomber targeted journalists covering an attack in central Kabul, killing nine.
Yesterday's attack underlined the danger in Kabul as elections approach next month, as well as the threat facing the Hazaras, a Persian-speaking minority that has long faced discrimination and which has borne the brunt of attacks claimed by Islamic State in Kabul.