A suicide bomber blows himself up outside a voter registration center in the Afghan capital Kabul, killing at least 57 people and injuring more than 100, in the most serious attack yet on preparations for elections scheduled for October.

The blast occurred when the bomber blew himself up among a crowd lining up to get access to an election-related registration site in a local school Sunday morning, spokesman Waheed Majroh tweeted.

Those among the dead were 21 women and five children while several wounded remained in critical condition.

The Afghan election officials have set Oct. 20 as the date for parliamentary and district councils' elections, which have been delayed for a couple of times over the past years.

The voter registration process started on April 14 for the polls.

The voters will cast their ballots to elect members of the 249-seat lower house of parliament for a five-year term while they will also elect members of district councils.

Afghan President Ashraf Ghani, Chief Executive Abdullah Abdullah and the UN mission in the county strongly condemned the attack, for which the Islamic State (IS) terrorist group has claimed responsibility.