A suicide bomber struck the convoy of Abdullah Abdullah, the front-runner in the first round of Afghanistan's presidential election, near the capital Kabul.
Four civilians were killed in the explosion and some of Abdullah's guards were wounded, but the candidate himself has no injuries, as Al-Jazeera English reports citing a televised statement he made shortly after the incident.
Taliban insurgents threatened Monday to attack Afghanistan's run-off presidential election, warning voters to stay away from polling stations for fear of injury or death.
Afghans are due to go to the polls on June 14 to choose whether Ashraf Ghani or Abdullah Abdullah should succeed President Hamid Karzai.
Athens Mayor Giorgos Kaminis on Friday chided Aris Spiliotopoulos, his New Democracy rival in Mays local elections, after the deputy likened Athens to Kabul in the wake of Thursdays bomb explosion outside the Bank of Greece.
He is undermining the citys effort to improve in terms of tourism, Kaminis said on Skai Radio.