Fifteen people, including five US soldiers, were killed on Friday by a car bomb and in attacks on voting stations and security forces across the country.
In Baghdad, troops imposed extra security measures that will see a 7pm to 6am ban on driving cars enforced until Monday, along with a strict ban on people venturing near polling centres except during the polls on Sunday.
Baghdad airport and Iraq's borders with its six neighbours will also be shut on Saturday on the eve of the vote for a 275-member parliament to form a post-Saddam Hussein government.
US forces intensified their presence on the Iraqi-Syrian border, with military helicopters carrying marines into the region, reported Aljazeera.
A US officer said the aim of the reinforcement was to prevent armed men entering Iraq from Syria.
In several sensitive areas of the country, foreign workers have been asked to leave.
Iraqi police will guard polling centres and the national guard will form an outer ring. US forces and the Iraqi army will make up a second ring of security on the edges of major cities.
Polling stations will be guarded
by Iraqi police
Cars will be banned from the sealed-off zones in an effort to prevent bombs, and voters will be searched before entering polling stations.
In the north, Mosul's governor imposed a four-day vehicle ban in the city, while shops have been ordered shut in the historical centre of the Shia shrine city of Najaf.
In all, more than 100,000 Iraqi police and soldiers have been deployed across the country to enforce election-day security.
The Iraqi military's chief of staff, General Babakir Zebari, expressed confidence about his soldiers' performance on election day, but said he would have preferred delaying the election.
Meanwhile, the Iraqi government announced on Friday that it had arrested two close aides of the al-Qaida-linked Abu Musab al-Zarqawi, one of whom was described as his Baghdad commander.
Bomb at power station
Violence continued on Friday. Four people were killed in a car bomb attack at a power station in the southern Baghdad neighbourhood of Dura, police and medical sources said.
A power station in Baghdad was
attacked, killing four people
"At around 9am (0600 GMT), a black GMC approached the checkpoint at the entrance of the power plant. There was only a driver inside the car, his face was masked," said a police officer who witnessed the attack.
"He was stopped at the checkpoint and a few seconds later, the explosion went off. We lost three comrades and one civilian was also killed in the blast," said the officer.
In the western city of Ramadi, a stronghold for resistance groups, six Iraqi soldiers were killed in ambushes, an Iraqi officer said.
US soldiers killed
A roadside bombing killed three US soldiers in a western district of the Iraqi capital on Friday afternoon, an American military spokesman said.
Earlier, two US soldiers were killed and three others wounded in two separate attacks on Friday in Baghdad, the US military said.
A bomb detonated about 2pm (1100 GMT) in southern Baghdad, killing one task force Baghdad soldier and wounding three others, the military said in a statement.
It announced separately the death of another soldier in an attack by small-arms fire in northern Baghdad.
A US helicopter crashed on Friday in the Baghdad area, the US military said, adding that it did not appear to have been caused by hostile fire.
Polling station attacked
A car bomb went off near a school to be used as a polling station in the same Baghdad neighbourhood where the power station was targeted.
A car bomb exploded near a
polling station in Baghdad
A police officer said the blast had caused material damage, but no casualties.
Attacks by resistance groups have caused frequent power cuts and fuel shortages and disrupted the water supply, denting US hopes that reconstruction would win the hearts and minds of Iraqis.
"The insurgents have conducted a fairly sophisticated,
apparently well thought-out campaign against infrastructure,
particularly around Baghdad - oil, electricity and water are
being interrupted by attacks on these facilities," said Bill
Taylor, a senior US embassy official in Baghdad.