Afghanistan's government says drug smugglers -- not the Taliban or al-Qaida -- were likely behind Wednesday's assassination attempt on interim President Hamid Karzai's vice presidential running mate.

Two people were killed and at least five others were injured, when attackers detonated a bomb as Ahmad Zia Masood's motorcade passed in the northern city of Faizabad.

A spokesman for the ousted Taliban regime is reported to have claimed responsibility for the attack. But Interior Minister Ali Ahmad Jalali said evidence gathered so far indicates the attackers were part of the drug mafia in Afghanistan.

Wednesday was the last day of campaigning before Saturday's presidential election. Officials have warned of a possible rise in attacks by remnants of the ousted Taleban and their allies in the run-up to the election.