U.N. special envoy to Iraq Martin Kobler expressed concerns after more than 20 people were killed following attacks on an election rally in Baquba, north of Baghdad.
"Candidates must be able to campaign without fear of intimidation, threats or violence, and citizens must be able to freely participate in electoral campaigns, without fear of being targets of deadly attacks," he said in a statement.
Kobler said last week he got assurances from the Independent High Electoral Commission that all provinces, excluding the three Kurdish provinces and Kirkuk, were ready for elections April 20.
The Iraqi government announced March 19 that it was delaying elections in Anbar and Ninewa provinces for six months because of a declining security situation.
The elections will be the first since U.S. combat forces pulled out of Iraq in late 2011. A series of damning reports on the lack of progress in Iraq coincided with last month's anniversary of the U.S.-led invasion in 2003.
Kobler said Iraqis needed to ensure that next week's elections were free from violence.
"The security forces are responsible for protecting candidates and their supporters, just like they are responsible for protecting all Iraqis," he said.