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Rahmat Gul, Associated Press
Supporters of Afghan presidential candidate Abdullah Abdullah chant slogans during a protest in Kabul, Afghanistan, Friday, June 27, 2014. Afghanistan's security situation has been complicated by a political crisis stemming from allegations of massive fraud in the recent election to replace President Hamid Karzai, the only leader the country has known since the Taliban regime was ousted nearly 13 years ago.

KABUL, Afghanistan — Thousands of supporters of an Afghan presidential candidate who has alleged massive fraud in a runoff vote marched Friday in the capital, suggesting the resignation of a top electoral official did little resolve the political impasse roiling the country.

Abdullah Abdullah, who has suspended ties with the main election commission over the allegations, joined thousands of protesters gathered in front of the presidential palace. The protesters shouted that they would not accept fraud and that Abdullah will be the next president.

Abdullah has said his campaign monitors recorded ballot box stuffing and other irregularities in the June 14 vote pitting him against Ashraf Ghani Ahmadzai after the field was narrowed from eight candidates in the first round on April 5. Chief electoral officer Zia ul-Haq Amarkhail resigned Monday, denying any involvement in fraud but saying he would step down for the national interest.

But Abdullah, who garnered the most votes in the first round but failed to secure the majority needed to win outright, has maintained pressure and drew thousands of supporters into the streets of Kabul on Friday. Protesters pointed a finger at outgoing President Hamid Karzai, who was constitutionally barred from seeking a third term.

"Death to Karzai," the crowds chanted, waving Afghan flags. "Karzai we know you are behind the fraud."

Karzai, the only leader it has known since the 2001 U.S.-led invasion that ousted the Taliban, has denied any involvement in vote rigging and set Aug. 2 as the date for the inauguration of a new leader in a bid to show he is not seeking to hold onto power. According to the election commission's official timetable, preliminary results are due on July 2 and final results on July 22.

Shopkeeper Ahmad Bashir said he and his entire family voted for Abdullah. "I hope the (Independent Election Commission) will stop the fraud... But if it doesn't listen to our demands we will hold another protest. It's our legitimate right."

The standoff has undermined Western hopes for a smooth transfer of power ahead of the withdrawal of most foreign troops by the end of this year. Both candidates have promised to sign a security pact with the Obama administration that would allow nearly 10,000 American forces to remain in the country in a training capacity and to conduct counterterrorism operations. A disruption in the announcement of election results could mean another delay in finalizing that agreement, which was rebuffed by Karzai.

The next president will preside over a country that is still very much at war, with near-daily attacks on security forces and civilians, most blamed on Taliban insurgents.

A bomb stuck to a police car exploded, wounding five policemen Friday in Gardez, the capital of eastern Paktia province. A roadside bomb then struck a police car responding to the attack, killing two policemen and wounding 10 other people, including five civilians, provincial police chief Gen. Zalmai Oryakhail said.

Oryakhail said the attacks came a day after police backed by NATO airstrikes launched an operation in the province's Sayed karam district, killing 29 Taliban fighters.

Six police also were killed and a seventh seriously wounded when a roadside bomb struck their vehicle late Thursday in the southern Kandahar province, police spokesman Zia Durrani said. In a separate incident, a district governor and his bodyguard were killed early Friday while riding on a motorcycle, the spokesman added.

In the southern Oruzgan province, authorities found the bodies of 10 Afghan police who went missing earlier this week, according to district governor Abdullah Khan.

The Taliban have stepped up attacks as part of their annual summer fighting season. A fierce weeklong assault in the southern Helmand province has killed dozens of people.

The U.S. Department of Defense also identified an American Marine who was killed Wednesday while conducting combat operations in Helmand. He was Sgt. Thomas Z. Spitzer, 23, of New Braunfels, Texas.

Associated Press writer Mirwais Khan in Kandahar, Afghanistan contributed to this report.