A suicide bomber blew himself up in an area in the north of the Afghan capital Kabul on Saturday.
Ten civilians and five police officers were killed when the bomber tried to enter a polling station and more than 25 were wounded, a senior security official said.
The attack appeared to have been the most serious of a day marked by a series of smaller-scale incidents that caused dozens of casualties across the country.
There was no immediate claim of responsibility.
The blast came as voting was still going on in parliamentary elections that authorities had feared would be a target for militant attacks.
Voting should have been concluded by the time the attacker struck in an area to the north of Kabul, but polling stations were kept open longer than normal to cope with large numbers of people who had been unable to vote.
It follows news that voting in Afghanistan’s parliamentary election will be extended to Sunday in some constituencies after technical and organizational problems stopped voters casting their ballot in some polling centres on Saturday, government officials said.
Taliban militants have issued a series of statements telling people not to take part in what they consider a foreign-imposed process and warning election centres may be attacked.
Wider election concerns have centred on technical and organisational problems with biometric voter-registration equipment, polling stations not opening on time, missing election materials and delays forcing lengthy waits.
Abdul Badi Sayad, chairman of Independent Election Commission said the voting process will continue until Sunday and will happen in locations where election officers or election material arrived late.
Confusion over biometric voter registration equipment, polling stations not opening on time, missing election materials and delays forcing lengthy waits added to tensions among voters desperate to cast their ballots.
The Taliban and Islamic State (IS) had both called for a boycott of the vote and threatened voters and candidates in the run up to election day.
Several security incidents marred the polling day, with more than 30 incidents recorded.
In the northern city of Kunduz 53 people were wounded and three killed in various incidents.
In Nangarhar in the east, seven people were wounded in a blast and Ghor in the west at least 11 police were killed.