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 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 Nematullah Shahrani.

Massoud was not harmed in Wednesday's attack, but the incident cast a pall over what was otherwise a lively and upbeat final day of the month-long presidential campaign. The vote is scheduled for Saturday.

Early Wednesday, an ebullient though closely guarded Karzai addressed a rally of about 5,000 supporters in the national stadium in Kabul, 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 atan dancers who whirled and dived in circles on the infield 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, who withdrew as a presidential candidate, and Ahmed Wali Massoud, a politician who is the brother of both Ahmed Zia Massoud, the vice presidential candidate, and the guerrilla leader Ahmed Shah Massoud, who was assassinated in 2001.

After darkness fell, Karzai held a brief news conference at his palace compound, flanked by Gailani and Pir Sayed Gailani, the elderly leader of their prominent religious family. The president brushed off questions about security concerns in the wake of the attack on Ahmed Zia Massoud, which came 21/2 weeks after a rocket was fired near Karzai's helicopter during a campaign tour.

"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.

"With full knowledge of the difficulties surrounding this exercise, we deem the degree of freedom and fairness adequate to allow the will of the Afghan people . . . to translate at the polls, and the next president to claim to represent the nation," said Jean Arnault, the U.N. special representative in Afghanistan.

U.N. officials, the U.S. Embassy and other observers here have warned that violent attacks may occur on election day, despite the presence of 18,000 American troops, 8,000 NATO troops, 17,000 Afghan soldiers and 28,000 national police officers across the country.

During most of the month-long campaign, few candidates have ventured out of their home areas or held public rallies. At times, the entire process has seemed reduced to closed-door negotiations instead of an open contest among 18 candidates.

But Wednesday, the Afghan capital finally caught the campaign spirit. Taxis draped with posters plied the streets, while loudspeakers blared the candidates' messages. Spontaneous mini-rallies formed, with participants marching a few blocks.

For sheer dazzle, the highlight of the day was a midafternoon rally in the national stadium for Gen. Abdurrashid Dostum, the ethnic Uzbek militia leader who is running for president. Dostum arrived in a Mercedes but soon switched to a snorting brown stallion -- his campaign symbol -- which he rode around the infield.

The rally was effusive and chaotic, with little security and lots of loud music. In contrast, Karzai's morning rally was held under rigid restrictions, with journalists separated from supporters on the field and the president appearing only inside a gated and guarded section of the upper reviewing stand.

Many in the crowd were students who had been brought in buses from their dormitories or older people who had been told by their community leaders that they should attend. Several carried pro-Karzai banners that had been handed to them outside the stadium -- and that some were unable to read.

"I don't know anything about the election. I came out of my house this morning, and people said, 'We are going to the stadium,' " said Mohammed Zaman, a white-bearded man who was wandering in the infield. "I didn't sign up to vote. Only God knows who can make a good and bad ruler."

Some students were well-informed, though, and listed numerous reasons they supported Karzai.

"He's a good man because he did not bring fighting to our country. He was not involved in destruction, and his hands are not bloody," said Hekmatullah, 19.

After delivering his speech, Karzai waved to the crowd and vanished down a stairwell in the stands, pursued by anxious armed guards. He reappeared at a stadium entryway and began shaking hands, but the crowd surged forward with a cheer and the guards insisted that he retreat to safety.