Baghdad, Iraq ? The lights went out just after Iraqis finished their sunset meal ending the day’s Ramadan fast. Huge swaths of Baghdad went black. Surrounding towns were covered in darkness. As the hours without power dragged on, water began to run out in some homes.

Sunni-led insurgents found a way to strike Friday on the eve of Iraq’s landmark vote on a new constitution despite the heavy clampdown imposed in towns and cities around the country by Iraqi and U.S. forces to assure Iraqis that it is safe to go to the polls.

Still, it was not a suicide bombing or a car bomb ripping through a market, as has happened in days leading up to the vote – suggesting security measures may have hampered militants from operating in the cities.

Instead, they hit 180 miles north of Baghdad, knocking out electricity towers that carry the lines through the unprotected countryside. Electricity Ministry workers were rushing to repair the damage and restore power, and by midnight – six hours after the lights went out – electricity was returning to parts of Baghdad.

The ministry could not guarantee all would be back to normal by the time polls open today. That will not effect the actual casting of votes – which is done by paper ballots, not machines – but the strike could intimidate some Iraqis from going to the polls.

Iraqi Interior Ministry special forces on Friday patrol the streets of Baghdad, Iraq, as U.S. and Iraqi forces stepped up security across the country and prepared to impose an overnight curfew in an effort to reduce insurgent attacks.

For most of the day, Iraqis remained home, with the streets of the Iraqi capital almost empty hours before a 10 p.m. curfew, and the country sealed off from the outside world as borders and airports were closed ahead of the vote.

In recent weeks, Sunni-led insurgents have waged a campaign of violence that killed hundreds, hoping to scare Iraqis from voting on the constitution.

The approximately 140-article charter – hammered out after months of bitter negotiations – is supported by a Shiite-Kurdish majority but has split Sunni Arab ranks after last-minute amendments designed to win support among the disaffected minority.

In Friday sermons across the nation, the message from Shiite pulpits was an unequivocal “yes,” but it was not so clear-cut in Sunni Arab mosques – varying from “yes,” “no” and “vote your conscience.”

Insurgents, meanwhile, detonated a bomb outside the Sunni Islamic Party’s office in central Baghdad, then set fire to the party’s main office in Fallujah. Nobody was injured in what were apparently symbolic attacks against that group’s recent decision to support the charter.

Today’s referendum, a key stop in Iraq’s passage to democratic rule that the U.S. hopes will pave the way for withdrawing foreign troops, takes place as American and Iraqi forces battle an enduring Sunni-led insurgency in Baghdad and areas to the west and north.

“Besides Allah, we need this constitution to protect us,” said Rajha Abdul-Jabar, a 49-year-old Sunni Arab mother of five married to a Kurdish dentist. “I, my husband and our children will go and vote yes tomorrow,” she said in the small convenience store she runs.

Kurds, a sizable minority that is mainly Sunni, fully support the charter.

Jameel Safar, a 30-year-old Kurd in Baghdad, said the charter will safeguard Iraq’s unity, but later added: “The Kurds are entitled to everything. We have a right to our own nation like everyone else.”

Tens of thousands of Iraqi army troops and policemen, meanwhile, formed security rings around the nation’s estimated 6,000 polling stations and set up checkpoints on highways and inside cities.

The capital’s streets were virtually deserted by late afternoon. Most shops did not open at all. Those that did closed early. Lines of cars a mile long waiting to fill up at gas stations provided one of the few signs of normalcy.

Ratification of the constitution requires approval by a majority of voters nationwide.

However, if two-thirds of voters in any three of Iraq’s 18 provinces vote “no,” the constitution will be defeated, and Sunni Arab opponents have a chance of swinging the ballot in four volatile provinces – Anbar, Nineveh, Salahuddin and Diyala.

Iraq’s Kurdish President Jalal Talabani and Shiite Prime Minister Ibrahim al-Jaafari appeared on television late Friday to make last-minute appeals for a “yes” vote.

Most of Iraq’s Shiites, about 60 percent of an estimated 27 million population, were expected to approve the charter, especially after Shiite spiritual leader Grand Ayatollah Ali al-Sistani called on followers to do so.