Potential fraud has become a key theme of Afghanistan's presidential race, with two of the three main contenders warning against attempts to rig the April 5 vote to benefit President Hamid Karzai's favored candidate, who firmly rejected such accusations.
An election perceived as stolen could plunge the country into fresh conflict just as U.S.-led international forces withdraw, foreign aid shrinks and Taliban attacks persist.
All the main candidates say they want to sign a security agreement with the U.S.—which Mr. Karzai has blocked—that would allow some American forces to remain after December. Turmoil over a disputed election, however, could disrupt those plans, too.
While Kabul officials deny bias or plans to stuff ballot boxes, the possibility that the election's legitimacy will be thrown into doubt is increasingly worrying the U.S. and allied governments that have spent hundreds of billions of dollars on Afghanistan since 2001.
"The responsibility of the candidates is extremely important. If Afghanistan, God forbid, will be destabilized again, nobody will be a winner," former Foreign Minister Zalmai Rassoul, seen as Mr. Karzai's presidential pick, said in a Wall Street Journal interview.
"The worst scenario would be that the election will not go well," he said. "The Afghan people will lose all the trust in the democratic process and we will go back to square one—instead of the ballot box, the people will use their Kalashnikovs to take power.