Officials urged Afghans on Saturday to defy Taliban insurgents and powerful warlords by turning out in force for Sunday's landmark parliamentary elections despite a wave of rebel attacks that killed 12 more people.

Security forces reported thwarting an attempt to blow up a big dam in the south and three other bomb plots, underlining the threat to a ballot aimed at bolstering Afghanistan's fragile democracy and marginalizing insurgents after decades of bloodshed.

Top U.N. envoy Jean Arnault (search) said militants failed to disrupt poll preparations with a surge of fighting that has killed more than 1,200 people the past six months, including seven candidates and four election workers.

"We are very confident that those extremists will also fail to disrupt and derail voting day," Arnault said at a news conference. "The Afghans will not let anyone stop them from participating in this election."

Some 12.4 million people registered to vote in Afghanistan's first parliamentary elections in more than 35 years — a span during which the country has been scarred by a Soviet invasion, a devastating civil war and the oppressive rule of the Islamic hard-liners of the Taliban.

Voters also will choose 34 provincial councils.

Coming 11 months after Afghans flocked to polling places in defiance of insurgent threats and elected Hamid Karzai as president, the ballot is the last formal step in instituting a democratic system envisioned when a U.S.-led coalition drove the Taliban from power in 2001 for harboring Osama bin Laden (search) and Al Qaeda (search) camps.

A U.S. military spokesman, Col. James Yonts, predicted "a massive number" would vote Sunday.

"This election will send a powerful message to the Taliban that their influence is waning and that the overarching grip they've had on this country for several years is no longer there," he told The Associated Press.

The comment came a day after a Taliban call for an election boycott. Taliban fighters said they would not attack civilians going to vote but would target areas where U.S.-led coalition forces are deployed.

Militants ambushed a security patrol on the outskirts of Kabul, killing a district police chief and two officers in the first attack so close to the capital in some time, Interior Ministry spokesman Luftullah Mashal said.

"The Taliban (search) and Al Qaeda are trying their best to create problems," Mashal told AP.

Security forces aided by U.S.-led coalition troops captured 20 militants as they laid explosives trying to blow up the hulking Kajaki Dam in southern Helmand province, Defense Ministry spokesman Gen. Mohammed Saher Azimi said. Thousands of people live nearby.

Mashal said government forces also stopped planned car bombings in volatile Ghazni and Paktika provinces and a fourth bomb plot near the border with Pakistan, where two Pakistanis suspected of being Taliban members were caught with explosives.

Guerrillas ambushed a patrol on the highway linking Kabul with the southern city of Kandahar, triggering a firefight that killed seven militants, local government chief Gulam Rasool said. He said a rebel rocket set a police car on fire, but the officers escaped.

The U.S. military said it had discovered seven roadside bombs across the country.

About 100,000 Afghan police and soldiers and 30,000 foreign troops were on alert to guard the election. In Kandahar, the former Taliban stronghold, all vehicles were banned from driving after midday Saturday due to car bomb fears.

In Pakistan, thousands of soldiers stood by near the border with Afghanistan. Militants based on the Pakistani side of the mountainous frontier are believed to cross into Afghanistan to stage attacks.

Amid the violence and concerns about voters being pressured by local warlords, the chairman of the Afghan-U.N. electoral body, Bismillah Bismil (search), assured voters their ballots would be secret.

"Do not be intimidated or frightened by the empty threats of those who attempt to influence your vote," he said.

Arnault, the U.N. envoy, hailed the election as a victory over violence.

"We are seeing today an unmistakable confirmation that there is in the country the emergence of a new political culture," he said. "A sense that the legacy of the rule of the gun can be resisted is now taking root."