At least 20 Iraqi security officers have been killed in two suicide car bombings near Ramadi and Samarra.
Iraq faced at least three separate bombings on Saturday
Sixteen died and up to 50 others were wounded in a blast at a police training base 230km (140 miles) west of Baghdad.
Soon after, a suicide bomber killed four Iraqi national guards and injured six in a blast at a checkpoint near Samarra, north of Baghdad.
Meanwhile Iraqi Defence Minister Hazim Shaalan said he had renewed contact with civic leaders in Falluja.
Mr Shaalan said he had spoken by telephone to the chief negotiator in the troubled city, Khaled al-Jumaili, and was hopeful that formal talks would begin soon to try to avert a full-scale military assault on the city.
The talks were broken off more than a week ago after Prime Minister Iyad Allawi threatened an attack if it failed to hand over Jordanian militant Abu Musab al-Zarqawi.
Earlier US forces said they seized a senior militant associated with Zarqawi in a pre-dawn raid on Falluja.
In other developments:
- Militant group Ansar al-Sunna says it has beheaded an Iraqi man captured in the northern city of Mosul and posts photographs of his dead body on its website
- Gunmen fire on a Turkish convoy in Mosul, killing two drivers and wounding two others
There are reports of a mortar attack in Baghdad's heavily fortified Green Zone, though there are no known casualties
Reuters news agency reports the bombing of two oil pipelines and a mortar attack in central Baghdad killing two civilians
Five US soldiers are injured in a bomb attack on the main highway from central Baghdad to the airport.
The BBC's Claire Marshall in Baghdad says the recent spate of attacks is a stark reminder of the task facing the US-led coalition and the Iraqi interim government, and illustrates the size and capability of the insurgency movement.
Pentagon officials have begun to say privately that the insurgency is now believed to be have more than 20,000 fighters throughout Iraq, our correspondent says.
The alleged senior militant detained by the US reportedly only recently moved into a top position in Zarqawi's Tawhid and Jihad group, following the death or capture of other leaders.
The group has been blamed for hostage beheadings and suicide bombings, including an attack that left 30 children dead.
The Associated Press news agency quoted local residents as saying the man's name was Abdel-Hamid Fiyadh, 50, adding that his sons Walid and Majid were captured with him.
He had no connection with Zarqawi, they said.
But the arrest prompted the US military to describe Falluja as a shrinking haven for Zarqawi's group.
"Zarqawi followers are starting to move to outlying areas of
Falluja in a continuing attempt to hide amidst the civilian
population of Falluja due to precision strikes against Zarqawi
hideouts and fighting positions," it said in a statement, quoted by Reuters.
US planes bombed Falluja on Friday night in a continuing effort to regain control of the city, a stronghold of resistance.
Two people were killed and three injured in the bombing, Reuters reported.
Zarqawi is believed to be using the city as a base, but city leaders have denied that he is even in Falluja.
Arabic TV carried a statement by the Falluja Mujahideen Shura Council saying reports about his presence there were "mere lies".