KABUL, Afghanistan - A roadside bomb exploded Wednesday afternoon under a convoy carrying one of President Hamid Karzai's two running mates in the upcoming presidential election. The attack, in remote Badakshan province, killed one man and injured five others, including a former Badakshan governor.

Officials said they had no idea who had carried out the attack on Ahmed Zia Massoud's convoy, which occurred in a relatively peaceful area of far northeastern Afghanistan. They said a bomb or mine was detonated as the vehicles were passing. A similar incident occurred in northern Kunduz province last month, when a bomb exploded under a convoy carrying Vice President Nemayatullah Shahrani.

Massoud was unharmed in Wednesday's attack, but the incident cast a pall over what was otherwise a lively and upbeat final day of the monthlong presidential campaign. The vote is scheduled for Saturday.

Early on Wednesday morning, an ebullient though closely guarded Karzai addressed a rally of about 5,000 supporters in the National Stadium, telling them, ''Your free vote is not just for president, it is for peace and stability for the future of Afghanistan.''

The crowd included traditional dancers who whirled and dived in circles to the rhythmic rumble of drums and a classical singer who sat cross-legged, squeezed his ancient harmonium and composed satirical political ballads on the spot.

Karzai said he was proud to see other candidates freely running against him and urging people to ''elect your president without fear.'' He also said he did not want to receive any votes as a result of pressure or bribes.

The president, already heavily favored to win the most votes, picked up several important endorsements Wednesday, including those of Ishak Gailani, a rival candidate from a prominent religious family, and Ahmed Wali Massoud, a politician who is the brother of both Ahmed Zia Massoud and the guerrilla leader Ahmed Shah Massoud, who was assassinated in 2001.

Karzai held a brief news conference at his palace compound, flanked by Gailani and Pir Sayed Gailani, the elderly religious leader of his family. The president brushed off questions about security concerns.

''An election is a time of tension in advanced countries, too. This is the first time for an Afghan presidential election after 30 years of hell,'' he said. ''Today's bombing was dastardly and wrong, but once the elections are over, the security environment should change drastically and improve.''

Despite the attacks on officials and candidates and a recent series of armed assaults in southern Afghanistan by the Taliban Islamic militia, which has vowed to disrupt the elections, the senior U.N. official here proclaimed Wednesday that Afghanistan was ready to hold the balloting as planned.