BAGHDAD: Under a blanket of tight security designed to thwart insurgent attacks, Iraqis went to the polls Sunday in an election testing the ability of the country's still-fragile democracy to move forward amid uncertainty over a looming U.S. troop drawdown and still jagged sectarian divisions.

Almost 20 million voters are eligible to turn out for the election, only the second vote for a full term of parliament since the 2003 U.S.-led invasion seven years ago this month. About 6,200 candidates are competing for 325 seats in the new parliament.

Insurgents have vowed to disrupt the elections — which they see as validating the Shiite-led government and the U.S. occupation — with violence, and Baghdad police said three people were killed in early morning violence when two mortar shells landed in a neighborhood in northeastern Baghdad.

Insurgents also launched three mortars toward the Green Zone — a heavily fortified area home to the U.S. Embassy and the prime minister's office — almost perfectly timed to coincide with polls opening at 7 a.m. across the country, Baghdad police said.

But security was very tight across the capital where only select authorized vehicles were allowed on the streets and voters headed to the ballot box on foot. The borders have been sealed, the airport closed and hundreds of thousands of Iraqi military and police flooded the streets.

Additional checkpoints were set up across the city, and in some parts of central Baghdad, people could not go 50 yards (meters) without hitting another checkpoint.

But in keeping with the U.S. military's assertion that these elections are an entirely Iraqi show, the only visible American military presence was a lone helicopter hovering over central Baghdad.

The U.S., which has lost more than 4,300 troops in the nearly seven-year conflict, has fewer than 100,000 troops in the country — a number that is expected to drop to about 50,000 troops by the end of the summer.

Exiting the polls, Iraqis could be seen waving purple-inked fingers — the now-iconic image synonymous with voting in this oil-rich country home to roughly 28 million people.

At one polling place in Baghdad's Karradah neighborhood, draconian security measures were in place with the school ringed by barbed wire, armed guards around the perimeter, and police using metal detectors to scan prospective voters.

Despite the threats of violence and frustration that has set in after years of fighting and faulty government services, many Iraqis were still excited about the possiblity of voting in what many here consider a key election to determine their country's future.

In a mostly-Sunni enclave called Zubair, near the southern port city of Basra, Jaman Khalf waited along with his family near the polling center since 6:30 a.m. and was the first person to cast his ballot.

"We have come here looking for change. We hope that Iraqis will elect qualified people who will salvage us from the miserable situation we are living in. We want better services, and we want construction and this is the reaon we are voting," he said.

But in the city of Baqouba, a former flashpoint for violence, few people had turned out to vote so far and the streets were nearly empty. At one polling center, a school, prospective voters had to go through at least three rings of police security, getting searched by authorities every time. At least 30 people were killed in a series of bombs earlier this week in Baqouba.

The election has been viewed by many as a crossroads at which Iraq will decide whether to adhere to the sectarian politics — Shiites aligning with Shiites, Sunnis with Sunnis and Kurds with Kurds — that have defined its short democratic history. Or move away from the sectarian tensions that almost destroyed this Shiite majority country that was held down under Saddam Hussein's Sunni-minority rule.

Iraqis hope it will help them achieve national reconciliation at a time when the United States has vowed to stick to President Barack Obama's timetable that calls for the withdrawal of combat forces by late summer and all American troops by the end of next year.

Prime Minister Nouri al-Maliki is fighting for his political future against a coalition led by mainly Shiite religious groups — the Supreme Islamic Iraqi Council and a party headed by anti-American cleric Muqtada al-Sadr. He also faces a challenge from secular alliance led by former a secular Shiite, Prime Minister Ayad Allawi, who has teamed up with a number of Sunnis in a bid to claim the government.

President Jalal Talabani was among the first to vote Sunday morning in the Kurdish city of Sulamaniyah. Talabani's party, the Patriotic Union of Kurdistan, is enmeshed in a tight race with an upstart political party called Change which is challenging the two Kurdish parties who have dominated Iraqi politics for years.

"I call on the Kurds and all Iraqi people to turn out because it is a decisive election," Talabani said, speaking after casting his ballot.