A convoy carrying Vice President Nematullah Shahrani was the target of a roadside bomb attack Monday in northern Afghanistan, just four days after an attempt on President Hamid Karzai's life in the south.

The attack in Kunduz province, in which Shahrani was unhurt but one driver was injured, came as there were escalating threats from Islamic groups and others who seek to sabotage the country's first presidential elections, scheduled for Oct. 9.

In the southeastern province of Paktika, meanwhile, two American soldiers were killed in a gun battle with Islamic guerrillas. Three Afghan soldiers reportedly were beheaded in Zabol province, and a renegade Afghan militia leader in Pakistan warned that Afghan refugees there would be at risk of attack if they attempted to vote.

In a separate political development Monday that could dramatically affect the election, Karzai's former interior minister and chief rival for the presidency, Yonus Qanooni, publicly rejected a proposal by Karzai that they join forces in a future government and said he would announce his campaign platform on Tuesday.

"We haven't made any deals," Qanooni told several journalists, effectively confirming widespread reports that intermediaries for him and Karzai had been meeting in an attempt to bring him back into the president's camp. "The discussions we have had with the government were not satisfactory to us or the people of Afghanistan."

Karzai, in New York for the U.N. General Assembly session, told journalists Monday that he would not form a coalition government "under any circumstances" and said he had not made a deal with Qanooni. "I will not make deals with anyone," he said.

Qanooni, 43, is viewed as Karzai's only serious challenger in a field of 18 candidates. He had been part of Karzai's cabinet since the government was formed under a U.N. plan in December 2001 but decided to run against him in July after Karzai dropped a close Qanooni ally, Defense Minister Mohammed Fahim, as a running mate.

Karzai, 47, the U.S.-favored candidate, is considered unbeatable, but Qanooni's last-minute entry into the race raised fears that the election would fragment along ethnic lines, with Qanooni representing ethnic Tajiks against Karzai, a member of the larger Pashtun ethnic group.

As a result, a group of foreign diplomats and moderate aides to both men have been pressing for a rapprochement, and it was rumored over the past week that an agreement was imminent.

"There has to be an ethnic balance to implement a program of national recovery and rebuilding," said a source close to the talks. If the election were split between the two men, he said, "the fear is that there will be a weak government and a chaotic political scene."

But several sources said both Qanooni and Karzai had difficulty persuading their harder-line supporters to accept such a deal as the election approaches and political tensions rise. Karzai's departure Sunday for his trip to New York and Saudi Arabia left the political scene in the capital confused and uncertain.

"Some understanding must be reached, because Afghanistan is not prepared for political competition," a regional diplomat said. "The daggers have been drawn along ethnic lines, so extremists on both sides can hijack the agenda and the moderates like Qanooni and Karzai cannot control it. There is a real danger that the situation can get out of hand."

None of the candidates has campaigned much, and with the exception of formal manifesto readings at the Information Ministry, few public rallies or news conferences have been held. Foreign election experts here said many candidates lack basic political skills and few are capable of launching a national campaign.

"There is a clear lack of awareness about the election process," said Grant Kippen of the National Democratic Institute, a U.S.-funded agency that is promoting and monitoring the Afghan elections.

"It has been hard to engage the candidates, or even to get them to plan for election day itself," he said. "It's been a bit of a struggle."

But the most serious obstacle to a successful election, analysts say, is the lack of security. There are widespread fears of voter intimidation by local political or militia bosses and of attacks on candidates and polling facilities by the Taliban militia and other groups that oppose the elections.

During this year's voter registration drive, there were numerous assaults on registration workers, vehicles and sites. Twelve people were killed. On Aug. 29 a car bombing killed 10 people in Kabul, and on Thursday a rocket was fired at Karzai's helicopter near the city of Gardez. Now one of Karzai's two running mates, who he had said would be largely campaigning in his place, has come under attack.

Officials said Shahrani and other cabinet members were traveling between Kunduz and Takhar provinces when a remote-controlled explosion struck their convoy. They blamed al Qaeda-linked forces for the attack, which occurred in a relatively peaceful region that was the first to begin formally disarming Islamic militias last October.

At the same time, a flurry of threats have been issued by Taliban-affiliated groups and others based in Pakistan. Leaflets distributed Monday in the name of Gulbuddin Hekmatyar, a former Afghan official and fugitive militia leader now in Pakistan, warned an estimated half-million Afghan refugees there not to vote.

Both Hekmatyar and spokesmen for various groups purportedly linked to the Taliban have denounced Afghanistan's election as a farce orchestrated by the United States. One Taliban faction has said it would kill "all infidels" and anyone who helps the Kabul or U.S. governments.

Both the United States and NATO have agreed to send additional military forces to Afghanistan to provide security for the election supplementing the 5,000 international peacekeepers who patrol Kabul and about 16,000 U.S. troops stationed in the country. But security conditions are considered so dangerous that European countries have declined to send teams of election monitors; that could make the vote harder to protect and guarantee.

Yonus Qanooni, center, Afghanistan's former interior minister and a presidential contender in the election this fall, is shown at a memorial service for an Afghan vice president, Abdul Qadir, who was gunned down in 2002.Vice President Nematullah Shahrani was uninjured.