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KABUL, Afghanistan (CNN) -- Under the menacing threat of violence from the Taliban, Afghans headed to the polls on Thursday in the war-ravaged nation's second-ever national election.

In parts of the capital Kabul, where recent calm was brutally shattered with a series of bloody attacks leading up to election day, the streets were eerily empty early in the day, save extra security checkpoints. The Taliban has vowed to disrupt the voting and the risk factor may have been too high for some Afghans to leave home on election day.

Security remained a serious concern, prompting the government to order a ban on media coverage of incidents of violence in an effort to "ensure the wide participation of the Afghan people."

In strife-torn southern Afghanistan, hundreds of U.S. Marines and Afghan soldiers have moved in to protect voters against possible Taliban attacks.

But in other parts of Afghanistan that have largely been spared the daily drumbeat of car bombs, assassinations and whizzing rockets, higher numbers of voters were expected at the polls. In the central Afghanistan province of Bamiyan, an ethnic Hazara region brutalized under Taliban rule, thousands of voters cast their ballots inside tents.

The Taliban ruled Afghanistan from 1996 until the 2001 U.S.-led invasion and in recent months has staged an increasingly bloody insurgency. Afghanistan observers and experts said a high turnout would help marginalize the radical Islamist group.

"We're at a moment of truth," said Mark Schneider, senior vice president of the International Crisis Group, an independent advisory and analysis organization.

Incumbent President Hamid Karzai, dressed in his traditional purple and green striped robe, cast his vote shortly after the polls opened Thursday and had his finger stamped with indelible ink, a measure to thwart fraud.

"It's the second presidential and parliamentary elections in Afghanistan and I'm sure this will be for peace, for progress and for the well-being of the Afghan people," he said afterward. "And I request the Afghan people to come out and vote so that through their vote, Afghanistan can be a more secure, more peaceful and a better country."

Karzai's name appears on the ballot with 40 other candidates for president. His top rival is his former finance minister Abdullah Abdullah, who once served as a confidante of Ahmed Shah Massoud, the charismatic leader of the anti-Taliban Northern Alliance killed by al Qaeda. The other candidate who gathered steam in the campaign is former Finance Minister Ashraf Ghani, a Western-educated man who served as a World Bank analyst.

Karzai was named interim leader after the fall of the Taliban regime and won the 2004 election by a significant margin. His popularity, however, has waned in recent months as Afghanistan has been crippled by corruption and increasing bloodshed.

Both Abdullah and Ghani hailed anti-corruption measures and government transparency as centerpieces of their campaign platforms. nternational donors are helping pay for Afghanistan's $223 million electoral undertaking. Richard Holbrooke, the top U.S. envoy in the region, acknowledged earlier this week that staging an election in the midst of war was tough, but expressed optimism that Thursday's vote would showcase Afghanistan's fledgling democracy.

Watch preparations on election eve »