An Iraqi Interior Ministry source says at least 12 people were killed and eight wounded when an explosion destroyed a building in Baghdad Sunday during parliamentary elections.
An earlier blast in the capital as polls opened killed four people.
Iraqis are voting in an election seen as a key test of Iraq's ability to maintain security and conduct a smooth transition of power after the U.S.-led invasion in 2003.
Some 20 million eligible voters are choosing from more than 6,000 candidates for the country's 325-seat parliament.
Security is tight throughout the country, with tens of thousands of Iraqi soldiers and police officers patrolling the streets to prevent possible attacks.
Along with the deadly attacks Sunday in Baghdad, militants have targeted other polling locations in Iraq.
An al-Qaida-affiliated group, the Islamic State of Iraq, has warned that anyone who decides to vote will risk death. At least four people were killed Saturday in a car bombing in Najaf.
Security was stepped up in Iraqi cities, as well as along the country's borders with Iran and Syria ahead of Sunday's parliamentary vote.
The borders have been sealed, the airport closed and vehicles banned across the capital.
There are no clear frontrunners in Sunday's elections. Many voters likely will choose among the three major Shi'ite-led coalitions.
Iraqi Prime Minister Nouri al-Maliki's State of Law Coalition and former Prime Minister Ayad Allawi's Iraqiya bloc have both reached out to Sunnis and other minority groups.
A third Shi'ite coalition, the Iraqi National Alliance, has been playing up its sectarian profile and has strong ties to Iran. It has been getting support from followers of anti-American cleric Moqtada al-Sadr.
On Saturday, Sadr encouraged Iraqis to take part in the vote and give their support to those who can best serve the nation.
Millions of Iraqis living overseas in 14 countries, as well as Iraqi soldiers, police, medical staff, patients and prisoners, have already cast their ballots in early voting.
The poll is only the second parliamentary election in Iraq since the U.S.-led invasion that ousted Saddam Hussein in 2003. It is being monitored by the United Nations, the Arab League and various international groups, as well as some 200,000 Iraqis.
Unlike the previous national election in 2005 when Iraqi Sunnis boycotted the polls, many of them say they plan to participate.
Some information for this report provided by AP, AFP and Reuters.