BAGHDAD—Iraq's leading candidates made final appeals to voters and an influential anti-U.S. cleric unveiled a unique election-day strategy, on the final day of campaigning for Sunday's national polls.
Meanwhile, expatriate voters cast ballots in 16 countries Friday, a day after early polling was held for security forces, hospital patients and prisoners.
Mr. Maliki criticized Mr. Allawi for spending campaign time meeting with Arab leaders throughout the region, including Turkey. Mr. Allawi used his last campaign appearance to raise allegations of electoral fraud, saying he had filed complaints with the Iraqi election commission and the United Nations, and that the number and severity of violations raised questions about the legitimacy of the vote.
The result of the election, and whether it is perceived as free and fair, will shape Iraq's democracy and the U.S. role here in the coming years.
Shiite party leader-in-exile Muqtada al-Sadr has maintained a low profile throughout much of the campaign. But Friday, through a senior aide at a Baghdad rally, the cleric gave block-by-block voting orders to thousands of supporters, in an effort to outmaneuver his own coalition partners within the Iran-backed, predominantly Shiite Iraqi National Alliance.
The message showed how voting tactics and a grass-roots organization could deliver the controversial cleric a disproportionate share of Shiite votes and significant leverage in the next government.
A strong showing by Mr. Sadr's slate of candidates would be troubling for the U.S. The movement maintains close ties to Iran and has been a relentless critic of Washington.
Mr. Sadr, the son of one of Iraq's most revered former clerics, led armed resistance to U.S. troops in the aftermath of the American-led invasion in 2003. But he has been living in self-imposed exile in Iran since 2007.
At the Sadr rally Friday, Hazem al-Arraji, a top Sadr aide and a widely known senior Shiite cleric, reiterated the movement's support for armed resistance to U.S. forces in Iraq. In practice, however, Mr. Sadr's cadres have been mostly quiet since late 2008.
In the final week of the campaign, reports rippled through Iraq that Mr. Sadr would return just before the vote, and that the government had issued a warrant for his arrest. Representatives of his movement showed journalists a piece of paper they claimed was the arrest warrant.
Mr. Maliki's government said no arrest warrant had been issued.
On Friday, Mr. Sadr's aides distributed thousands of pamphlets directing Baghdad residents to vote for specific candidates for Mr. Sadr's Iraqi National Alliance. The directions broke out preferred candidates for 80 different areas in Sadr City, the Baghdad slum that has long been a Sadr stronghold.
Unlike the general election in 2005—Iraq's first after the fall of Saddam Hussein—voters this time are casting ballots for individual candidates rather than slates.
Any votes a candidate receives above the threshold needed to win a seat will be distributed to other candidates on the slate.
As a result, if too many people vote for the same Sadrist candidate, those votes could wind up going to other parties on the broader, Shiite slate, such as the Islamic Supreme Council in Iraq, or ISCI. Though allied for this election, Mr. Sadr's movement and ISCI are historically fierce rivals.
"We don't want to lose votes to candidates from other parties on our list," Mr. Arraji, the Sadr aide, told the thousands of followers who massed on a wide boulevard in Sadr City. "We want the Sadr bloc to be the dominant bloc on the list."
To avoid diluting their voting power among candidates who won't meet the seat threshold, Mr. Sadr's campaign strategists decided to run just one candidate for each seat.
Nearly every other party is fielding two candidates per seat as the law allows. Their assumption: The more candidates the broader list has on the ballot, the more overall votes it will garner as a whole.
Despite a string of attacks at or near Baghdad polling stations on Thursday, senior Obama administration officials said they believed the early round of voting went relatively well.
Since Iraqi security forces were voting early, the risk of attacks may have been higher than it will be on Sunday, they said. "They seemed to have passed the test [Thursday], at least," said one senior administration official.
The U.N. expected about half-a-million expatriates to participate in the voting on Friday. Voting in Syria and Jordan—countries that have taken in large numbers of Iraqis fleeing violence—appeared to go smoothly. In London, a fistfight broke out at one polling station, according to footage broadcast prominently by Iraqi satellite channels. The reason for the brawl wasn't clear.
—Ben Lando and Peter Spiegel contributed to this article.