Mike Hanna, Al Jazeera's correspondent in Baghdad, said: "At Friday prayers, although no campaigning, there were some sermons that could probably be classified as political."
He said the situation in the capital was calm and that a high turnout was expected, but added: "Events over the past few days have have indicated that despite the heightened security arrangements, the potential for violence remains."
A string of deadly blastsshattered an early round of voting on Thursday, killing 14 people and injuring 57 others.
"Terrorists wanted to hamper the elections, thus they started to blow themselves up in the streets," Ayden Khalid Qader, the deputy interior minister responsible for election-related security, said.
Strict security measures are coming into force - beginning with a curfew on Friday evening in the Iraqi city of Ramadi and other restrictions lasting three days.
These include the banning of civilian vehicles on election day.
Sunday's vote will be supervised by as many as 120 international monitors, with a number of foreign embassies providing staff to act as monitors too.
However, officials expect to see more violence in the run-up to the poll, and on election day.
Iraqis living abroad are voting in their country's general election, two days before the election.
Hundreds lined up at polling stations in Syria, home to the largest Iraqi expatriate community, most driven from their homeland by the violence and instability.
Iraqi nationals are also voting in Jordan, the United Arab Emirates, Iran, Turkey, Egypt, Lebanon, the United States, Britain, Canada, Denmark, Austria, Australia, Germany, the Netherlands and Sweden.
The expatriate vote is running from Friday to Sunday.
Al Jazeera's Nisreen el-Shamayleh, reporting from Amman, the Jordanian capital, said: "They [Iraqi voters] feel that these elections are very crucial and will be more democratic than the previous first parliamentary election held in 2005.
"Turnout at the polls is expected to be very high after the Friday prayers," she said.
The United Nations refugee agency estimates that more than 4.2 million Iraqis have fled the country since the 2003 US-led invasion.
The process of forming a new four-year Iraqi governmentafter Sunday's election will be long, difficult and possibly violent, US officials said on Thursday.
| A full-scale security clampdown is being rolled out in Iraq ahead of general elections [AFP]
"Given the stakes, given the efforts of people to secure political advantage, it would not be surprising to see violence during that period," one of the officials said, speaking to reporters on condition of anonymity.
There is no clear front-runner among the political parties in what the official called an "extraordinarily competitive"election.
"We expect the election and the government formation process thereafter to be very hotly contested, and we anticipate a difficult process of government formation that could take some time."
The new government will be in place as the US completes the withdrawal of its remaining troops by the end of 2011.
There are about 96,000 US soldiers stationed in Iraq, but that number is due to be reduced to 50,000 by the end of August 2010.
Speaking in Guatemala, Hillary Clinton, the US secretary of state, said she could not foresee a basis on which the US would adjust its timetable for pulling out its troops.
The Iraqi electoral commission is to announce preliminary results on March 10-11, based on votes from about 30 per cent of the polling stations.
The supreme court would then certify the poll results, after hearing appeals, within about a month of the election, the official said.
After the last national election in 2005,it took Iraq's feuding political parties about five months to agree on a prime minister and for a cabinet to be approved.