KABUL - An influential Afghan governor who had signalled his intention to run for president said Saturday he will not, leaving President Hamid Karzai in an increasingly strong position to win re-election.

Nangarhar Gov. Gul Agha Sherzai, who met with President Barack Obama last year when he visited Afghanistan before the U.S. elections, was seen as one of the few possible candidates who could have threatened Karzai's hopes for sealing another five-year term in the Aug. 20 vote.

Despite Karzai's declining popularity, no realistic challengers have emerged among the dozens who are likely to run. The deadline for candidates to register is May 8.

Karzai has led Afghanistan since soon after a U.S.-backed invasion ousted the hard-line Taliban regime from power in late 2001 in the aftermath of the Sept. 11 attacks in the United States. He swept Afghanistan's first post-Taliban election in 2004.

A spike in fighting against Taliban insurgents in recent years and a rising civilian death toll have eroded Karzai's standing, as have accusations from conservatives that he is a puppet of Western powers. His government is also widely viewed as corrupt and ineffective.

Sherzai's spokesperson, lawmaker Gul Khalid Pushtoon, told The Associated Press this past week that Sherzai had intended to register his candidacy on Saturday. Pushtoon said Friday that Afghanistan's top vice president -- Ahmad Zia Masood -- was breaking away from Karzai to join Sherzai on a competing ticket, although this was not confirmed by Masood's spokesman.

But after a private meeting with Karzai on Friday, Sherzai told reporters Saturday he would not run. He said, however, that he was resigning as Karzai's governor of eastern Nangarhar province.

A statement from Karzai hours later said the president did not accept the resignation. The statement welcomed Sherzai's decision not to run for president.

A spokesman for Karzai said he could not confirm whether there was any connection between the Karzai-Sherzai meeting on Friday and Sherzai's decision not to run for president.

"All I know is after that meeting Sherzai has decided he is not running for president and is resigning as governor, and President Karzai has said he does not accept the resignation," said spokesman Waheed Omar.

Sherzai, who met with Obama when he visited Afghanistan in July before becoming U.S. president, has a mixed reputation. He helped the U.S. oust the Taliban from southern Kandahar province in the first push against the militants in 2001, but has also been accused of heavy-handed rule and corruption in the aftermath.

More recently, Sherzai is credited with helping to eradicate opium poppies from Nangarhar province, one reason he is popular with U.S. officials.

Sherzai had in the past been a strong supporter of Karzai but Pushtoon said on Friday he would run against the president because they don't believe he's popular enough with the citizenry to hold onto the job.

Pushtoon could not reached for comment Saturday.