Campaigning has begun for next month's general election in Iraq, with Prime Minister Nouri Maliki seeking a third consecutive term in office.
No single bloc is expected to win a majority of the 328 seats in the Council of Representatives on 30 April.
However, Mr Maliki's Shia-dominated State of Law alliance is widely seen as the front-runner.
The poll comes with violence in Iraq at its highest level since the peak of the sectarian insurgency from 2006 to 2008.
On Tuesday, the UN mission in Iraq reported that a total of 592 Iraqis, including 484 civilians, had been killed in violent attacks in March.
The figures do not include casualties from the unrest in the western province of Anbar, where security forces are battling Sunni militants allied to the jihadist Islamic State in Iraq and the Levant (ISIS) who have controlled parts of the cities of Falluja and Ramadi since late December.
The stand-off was triggered by the Shia-led central government's decision to break up a Sunni Arab protest camp near Ramadi.
"With election day getting nearer, I once again stress the need for unity and a holistic approach to violence and terrorist threat in Iraq," said the UN envoy to Iraq, Nikolay Mladenov.
"The political, social and religious leaders of Iraq have an urgent responsibility to set up a mechanism for dialogue and conflict resolution between various stakeholders."
Although the government has not discussed postponing the election, it is unclear whether it is possible for voting to take place throughout Anbar.
The poll was put at risk last week when Iraq's election commissioners threatened to resign over what they said was political and judicial interference in their work.
The board of the Independent High Electoral Commission (IHEC) complained that that judges and parliament had issued contradictory rulings regarding the exclusion of certain candidates.
But after holding talks with Mr Mladenov, the commissioners on Sunday announced that they had decided to withdraw their resignations and resume their duties "in full confidence".
The dispute stemmed from divergent interpretations of the electoral law, which includes a clause allowing for candidates not "of good reputation" to be barred.
Mr Maliki has been accused of using the law to prevent his political enemies from standing.
Those disqualified by a judicial panel because they are subjects of arrest warrants include former Finance Minister Rafa al-Issawi and several other MPs who oppose the prime minister. Parliament says candidates must not be excluded unless they have been convicted.
Analysts say the strongest challenge to Mr Maliki's State of Law bloc next month is likely to come from rival Shia factions, rather than a large Sunni alliance.
The Iraqiyya bloc of former Prime Minister Iyad Allawi, which won the most seats in the last general election in 2010, has largely fragmented into components led by various Sunni and other leaders.