A bomb has exploded at a rally held by President Hamid Karzai's running mate in the northern Afghan city of Feyzabad, Afghan officials say.
Vice-presidential candidate Ahmad Zia Massoud was not hurt in the explosion.
Interior ministry spokesman, Lutfullah Mashal, told the AFP agency two people had been killed. Other reports said one person had died.
Mr Massoud is the brother of the late Ahmed Shah Massood, who led the battle against Soviet occupation.
Mr Mashal said: "The investigation is going on. It is the work of the enemies of peace and the elements who want to derail the election process."
He said there had been no arrests so far over the attack in Feyzabad, 300km north-east of Kabul.
The Taleban and al-Qaeda have vowed to disrupt the presidential elections which take place on Saturday.