Afghan President Hamid Karzai is expected to concede Tuesday that he did not win an outright majority of votes in August's presidential election.
U.N. election auditors announced Monday they are throwing out nearly one-third of Mr. Karzai's ballots because of fraud, depriving him a majority of the vote.
After accounting for the fraudulent votes, Afghanistan's election commission is expected to announce Tuesday that the final vote tally shows no outright winner, triggering a runoff.
International pressure has been building on Mr. Karzai to accept either a power-sharing coalition with his top challenger, Abdullah Abdullah, or to prepare for a runoff election.
It is not clear what option Mr. Karzai favors, but U.S. Secretary of State Hillary Clinton said Monday she has been "encouraged" by "the direction the situation is moving."
Afghanistan's fraud-ridden presidential election and weeks of political deadlock that followed have further undermined the already weak central government. Authorities worry that there may not be enough time to hold a run-off election before the onset of winter weather, possibly delaying a vote until spring.
While U.S. President Barack Obama has been waiting for the election results to announce his new war strategy, including the possible deployment of more U.S. troops, the U.S. defense secretary said Monday the strategy cannot wait until a new government is in place in Kabul.
U.S. Defense Secretary Robert Gates told reporters en route to Asia late Monday that working out allegations of fraud will be an "evolutionary process," and decisions about strategy and troop decisions should not wait until a new government to take office.
General Stanley McChrystal. the top U.S. commander in Afghanistan, is said to be asking the president for as many as 40,000 additional troops.
Meanwhile, in Afghanistan Tuesday, NATO forces announced they have closed a base in eastern Afghanistan's Nuristan province that was involved in one of the war's deadliest battles earlier this month.
NATO forces released a statement Tuesday saying troops handed over combat outpost Lowell in the Kamdesh district to local authorities, after removing all military equipment.
NATO said the closure was planned well before the October 3rd assault that killed eight American and two Afghanistan soldiers. Some 100 insurgents were also estimated killed in the clash.
Some information for this report was provided by AFP and AP.