BAGHDAD - A string of deadly blasts shattered an early round of voting in Iraq Thursday, killing 17 people and highlighting the fragile nature of the country's security gains ahead of crucial parliamentary elections this Sunday.

Iraq security forces were out in full force, trying to protect early voters in an election that will determine who will lead the country through the crucial period of the U.S. troop drawdown and help decide whether the country can overcome its deep sectarian divisions.

But three explosions - a rocket attack and two suicide bombings - showed the ability of insurgents to carry out bloody attacks. They have promised to disrupt the voting with violence.

"Terrorists wanted to hamper the elections, thus they started to blow themselves up in the streets," said Deputy Interior Minister Ayden Khalid Qader, responsible for election-related security across the country.

Thursday's voting was for those who might not be able to get to the polls Sunday. The vast majority of early voters were the Iraqi police and military who will be working election day - when the rest of the country votes - to enforce security. Others voting included detainees, hospital patients and medical workers.

A spokesman for the Independent High Electoral Commission, Muhammad Al-Amjad, said about 800,000 people were eligible to vote Thursday, although he had no figures on how many actually cast ballots.

Many of the blast victims were believed to be security personnel, targeted by suicide bombers who hit police and soldiers lined up to vote.

Convoys of army trucks and minibuses ferried soldiers and security personnel to and from polling stations. Many stores were shuttered, and normally crowded streets were nearly empty, as people stayed home on a holiday declared by the government.

In Washington, senior administration officials said a number of potential attacks were headed off by security forces on the perimeter of polling places Thursday. The officials, who spoke on condition of anonymity to discuss White House assessments of the voting, would not elaborate on attacks that were prevented.

They also said that so much was at stake in the election that the administration "would not be surprised to see violence" in the remaining days leading up to the election, on voting day or in the period during which a new government is being formed.

The officials also predicted it would be a matter of months before a new government is formed, but that would not affect long-standing U.S. plans to withdraw all combat forces by the end of August. There currently are under 100,000 U.S. troops in Iraq. After the combat pullout, the plan calls for 50,000 troops to remain in place as a protective force through the end of next year.

ISLAMABAD (AP) - Pakistani intelligence agents have arrested a senior Afghan Taliban commander, the latest move in a crackdown on the insurgent network in Pakistan.

Agha Jan Mohtasim, a former finance minister for the Taliban before the U.S.-led invasion in 2001, was detained in the southern city of Karachi, two intelligence officials said Thursday. One of the officials said two other Taliban associates were arrested along with Mohtasim, though he would not identify them.

The agents did not say when the arrests were made, and spoke on condition of anonymity because they were not authorized to give their names to the media.

Pakistan and Afghan officials have said at least four other Afghan Taliban leaders have been arrested in Pakistan in recent weeks, including the No. 2 leader of the movement, Mullah Abdul Ghani Baradar. The arrests have been hailed by U.S. officials and many analysts as a major blow to the Taliban in Afghanistan.