Officials say the suicide bomber targeted election candidate Saleh Mohammad Asikzai's campaign office in the southern city of Lashkar Gah in Helmand province. There was no immediate claim of responsibility for the attack.
An election candidate was among eight killed in a suicide attack in Afghanistan on Tuesday, officials said, days ahead of a parliamentary vote that militants have vowed to disrupt.
Another 11 people were wounded when the attacker blew himself up inside Saleh Mohammad Asikzai's campaign office in the southern city of Lashkar Gah, Helmand provincial governor spokesman Omar Zhwak told AFP news agency.
Asikzai, a young first-time candidate, was campaigning on a platform of "positive change".
Provincial police spokesman Salam Afghan confirmed the attack. "We are investigating," he said.
There was no immediate claim of responsibility for the attack, but Helmand is a Taliban stronghold.
It is not clear how many people were inside the room at the time of the blast, which comes a day after the Taliban warned candidates to pull out of the "bogus" election scheduled for October 20.
President Ashraf Ghani condemned the attack and said Afghans who believed in democracy would not allow "terrorists" to stop the elections.
'Malicious American conspiracy'
Describing the polls as a "malicious American conspiracy" and urging voters to boycott them, Taliban spokesman Zabihullah Mujahid said the militants would pull no punches to disrupt the ballot.
It was the second suicide attack to target a parliamentary candidate since campaigning officially kicked off on September 28.
An attack on a rally in the eastern province of Nangarhar on October 2 killed 13 people and wounded more than 40.
More than 2,500 candidates will contest the poll, which is seen as a test run for next year's presidential vote.
At least five have been murdered in targeted killings so far, according to the Independent Election Commission.
In other violence, "hundreds" of Taliban fighters stormed a military post in the northern province of Jowzjan on Monday, provincial police chief Faqir Mohammad Jawzjani told AFP.
At least 12 soldiers and 30 Taliban fighters were killed in the attack, he said.
Elections in turmoil
Preparations for the ballot, which is more than three years late, have been in turmoil for months and there has been widespread speculation about whether the vote would go ahead.
Bureaucratic inefficiency, allegations of industrial-scale fraud and an eleventh-hour pledge for biometric verification of voters threaten to derail the process and any hope of a credible result.
Some 54,000 members of Afghanistan's beleaguered security forces will be responsible for protecting more than 5,000 polling centres on election day.
More than 2,000 polling centres that were supposed to open will be closed for security reasons.