Preliminary voting began in Iraq Monday as violence killed 12 and militant groups issued a joint statement saying the balloting violated God's law.

Soldiers, patients and prisoners lined up and cast their ballots at select polling stations across the country, days ahead of the Dec. 15 election — when the rest of the country will go to the polls to select a constitutional parliament. At one Baghdad hospital, patients voted from their sick beds.

In a joint statement posted on the Web, Al Qaeda in Iraq and four other Islamic militant groups declared that no reconciliation with Iraq's U.S.-backed government had occurred and the elections were religiously prohibited.

The Iraqi government said a security plan would be in effect Tuesday to try to curb any possible violence aimed at disrupting the upcoming elections. The borders will be closed to non-essential traffic, a nighttime curfew will be extended in various places and checkpoints will be put in place to limit domestic travel.

U.S. officials hope the new parliament can help quell the Sunni-dominated insurgency so that American forces can begin heading home. The 275-member assembly will be the first full-term parliament, serving for four years, since Saddam Hussein's 2003 ouster.

"The reasons for the presence of the multinational forces will start to decrease," Prime Minister Ibrahim Al-Jaafari said of the elections.

But he said that a timetable for a withdrawal would also depend on the ability of Iraqi forces to take over security.

"We want the multinational forces to leave, but we don't want security to disappear as well," al-Jaafari said. "When the Iraqi hands are in complete control of the security situation in Iraq, then we will tell the multinational forces, 'Thank you. Please leave the Iraqi lands.'"

A new opinion poll found most Iraqis disapprove of the presence of U.S. forces in their country, yet they are optimistic about Iraq's future and their personal lives.

More than two-thirds of those surveyed oppose the presence of coalition troops, and less than half, 44 percent, say their country is better off now than it was before the war, according to an ABC News poll conducted with Time magazine and other media partners.

But three-quarters say they are confident about the parliamentary elections and more than two-thirds expect things to get better in the coming months, the poll said.

The Internet statement, which could not be authenticated immediately, said taking part in the election contradicted God's law, saying the only rules Muslims should follow are those in the Koran.

"To engage in the so-called political process and taking part in the renegade election are religiously prohibited and contradict the legitimate policy approved by God for the Muslims in their holy Koran," said the statement.

Another statement believed to be from an insurgent group said fighting would continue regardless of the vote. The unsigned statement, distributed in the Sunni stronghold of Azamiyah, said Sunnis could use the elections to battle corruption and make some political gains but that "fighting will continue with the infidels and their followers."

An empty minibus loaded with explosives blew up Monday near a hospital in Baghdad, killing three civilians and injuring 13, including five police officers, authorities said. Police Lt. Mohammed Khayoun said the van's driver abandoned it and ran.

A U.S. soldier was killed Monday in a bombing in Baghdad and another American soldier attached to the Marines died Sunday before in a suicide bombing near the city of Ramadi, the U.S. command said. The deaths brought to 2,144 the number of U.S. military members killed in Iraq since the war began, according to an Associated Press count.

Clashes between security forces and militants killed two police officers and injured nine, police said. Two other people were killed in a drive-by shooting in the southern Dora district of Baghdad.

Gunmen killed three men and injured a woman when they opened fire on a pickup truck with Education Ministry license plates.

In Muqdadiyah, about 60 miles north of Baghdad, a roadside bomb killed a woman and injured five other people.

Police also said a businessman and his 23-year-old son were kidnapped in Baghdad's upscale Mansour district.

Monday's early voting saw the first of 1,500 patients cast ballots at Baghdad's Yarmouk hospital, officials said.

"There is a big hall for patients who can easily walk and the election committee moves a box around to the wards where there are patients who can't leave their beds," said Yousif Ibrahim, director of the election center.

It was not be the only early voting ahead of general elections.

On Tuesday, the estimated 1.5 million Iraqi voters living outside the country can begin casting their ballots at polling centers in 15 countries. That voting also ends Thursday.

Suspected insurgents held in U.S. or Iraqi detention but who have not been convicted, are eligible to vote, Iraqi officials said. Saddam, who is jailed and facing trial for the deaths of more than 140 Shiites in 1982, also can vote but it is not known whether he would.

Most attention has focused on Sunni Arabs, who largely boycotted the Jan. 30 election to protest the continued U.S. military presence. That enabled the Shiites and Kurds to dominate parliament, a move that sharpened communal tensions and fueled the insurgency.

This time, more Sunni Arab candidates are in the race, and changes in the election law to allocate most seats by province instead of based on a party's nationwide total all but guaranteed a sizable Sunni bloc in the next assembly.

Turnout in January was about 58 percent but less than 5 percent in the predominantly Sunni province of Anbar, a hotbed of insurgency.

Even with a big Sunni vote, Shiites are expected to win the biggest share of parliamentary seats. Shiites form an estimated 60 percent of Iraq's 27 million people compared to 20 percent for the Sunni Arabs.

Some Sunni religious extremists, including Al Qaeda in Iraq, have warned Iraqis against voting. But most insurgent groups have avoided threats of violence that helped keep Sunni turnout low in January.

The Associated Press contributed to this report.