Interim Iraqi Prime Minister Iraq Iyad Allawi has said it will be impossible to provide full security for this month's parliamentary elections.
A wedding celebration became a scene of horror
Mr Allawi said the measures being put in place were not enough to prevent all attacks by insurgents.
He was speaking after two more suicide bombings apparently targeting Shias killed at least 25 people on Friday.
In the deadliest, at least 14 died when a car bomb exploded as worshippers left a mosque in the capital, Baghdad.
The bomber struck the al-Taf mosque as people were celebrating the festival of Eid al-Adha - one of Islam's most important holidays.
Some 40 injured - including children - were rushed to a nearby hospital.
Hours later, a vehicle reported to have been an ambulance exploded south of the capital, killing at least 11 people at a Shia wedding party. The bride and groom were among many more reported injured in the blast.
Shia political leaders think militants are trying to stir up sectarian strife. The blasts came after a notorious militant leader reportedly warned of a long fight against US forces in Iraq.
The latest attacks come amid an increase in unrest in the run-up to Iraq's elections.
Commenting on the violence during a phone-in TV show, Mr Allawi said: "The plan is not enough to confront the savage attacks."
Zarqawi has a US bounty of $25m on his head
He said the attackers would "try to make the political process fail" but expressed confidence that security services would "meet the challenges".
The BBC's Caroline Hawley in Baghdad says every aspect of Iraq's first direct national vote for decades is being overshadowed by violence.
There has been very little door-to-door campaigning because several candidates have been killed and many more threatened, she says, so this is an almost faceless campaign.
Iraq's most revered Shia cleric, Ayatollah Ali al-Sistani, has urged his followers to take part in the election, while some Sunni Muslim organisations have demanded a boycott.
In an audio recording posted on a Islamic website on Thursday, militant leader Abu Musab al-Zarqawi accused Shias of attacking and defiling Sunni mosques in Falluja "with the blessing" of Ayatollah Sistani.
The recording warned the fight against US troops and their allies in Iraq "could last months and years".
The US has offered a $25m (£13m) reward for Zarqawi, whose group is believed to be affiliated to al-Qaeda.