A key ally of Afghanistan's transitional president, Hamid Karzai, is defecting from the government to run against the Afghan leader in the upcoming presidential election.

Political intrigue marked the final day for candidates to register in Afghanistan's first post-war presidential election, slated for October.

Well-known Education Minister Younus Qanuni announced he had resigned from office to qualify as a contender in the presidential race. The move coincided with the resignation of President Karzai's powerful defense minister, Mohammed Fahim, who reports say plans to support Mr. Qanuni's rival bid.

Both men are key leaders of the Northern Alliance, a group of Afghan militias that joined forces with the United States in 2001 to oust Afghanistan's Taleban regime.

The resignations are allegedly a reaction to President Karzai's decision to drop Mr. Fahim as his senior of two running mates.

Instead, Mr. Karzai gave the post to Afghan diplomat Ahmed Zia Masood, whose brother Ahmed Shah Masood led the Northern Alliance until his assassination in September 2001.

In his nomination speech, President Karzai played up his running mate's connection to the fallen Northern Alliance leader.

"Mr. Ahmed Zia Masood, from a noble family of Afghanistan, from a noble legacy of Afghanistan of jihad and of sacrifice to this country, the brother of our martyred hero, Ahmed Shah Masood," he said.

The political tensions resulting from the last-minute maneuvering prompted international peacekeepers to tighten security around the capital, as their spokesman Commander Chris Henderson explains.

"We are taking prudent measures for security, in I think what is generally regarded as a time of political sensitivity," he said.

While foreign news media describe Mr. Karzai as an overwhelming favorite to win the election, many local politicians, including some of the president's supporters, see a tight race developing.

Other key candidates include Abdul-Satar Serat, an ex-justice minister closely associated with Afghanistan's widely popular former king. Mr. Serat had originally been chosen as Afghanistan's first transitional leader, but stood down in favor of President Karzai.

Also running is Ahmed Shah Ahmedzai, who carries a reputation as a religious-minded member of Afghanistan's mujahideen, or "holy warriors."

Dr. Masooda Jalal is the only woman running for president, though local media describe her as having little chance of winning.

Several ethnic candidates are also in the race, including Uzbek militia commander Abdul-Rashid Dostum and another northern military leader, Haji Mohammed Mohaqiq, who represents the Hazaras, a minority Shi'ite Muslim group.

If no candidate wins more than 50-percent of the vote, a run-off between the top two candidates will take place, tentatively planned for two weeks after the first round.