Iraq's Prime Minister Nouri Maliki has urged Iraqis to use the Muslim holy month of Ramadan to set aside their differences and seek national unity.
Mr Maliki urged Iraqis to live side by side "like brothers"
Mr Maliki said Iraqis could either live side by side as brothers, or see their country turned into an arena for the settling of political accounts.
His comments come as at least five people were killed in several car bomb attacks in Baghdad and elsewhere.
An insurgent leader has been captured with seven aides, the authorities said.
Mr Maliki's comments came a day after at least 35 people were killed in a car bomb attack on a kerosene tanker in Baghdad's mainly Shia district of Sadr City.
"I call on Iraqis to take advantage of this sacred month to reinforce brotherly ties to reject division and anything that threatens the Iraqi social fabric," he said.
"Either we live side by side in a spirit of brotherhood, not separated by ethnic or sectarian identifies, or Iraq becomes a battlefield for different groups to settle their scores."
Saturday's attack took place on the first day of Ramadan for Iraq's Sunni community and was one of the deadliest in Iraq in recent weeks.
The country's Shia religious authorities have said Ramadan will start on Monday.
In recent years, Iraq has seen a rise in violence during Ramadan.
In other violence:
- In Baghdad, one car bomb attack targeted an Iraqi army convoy, killing at least two people; another was aimed at a police patrol, and killed at least one person
- A suicide car bombing killed two Iraqi soldiers and wounded at least two, when the driver rammed his car into their checkpoint in the town of Tal Afar, 420km (260 miles) north-west of Baghdad
- Gunmen killed police Col Ismail Jihayan late on Saturday in Tikrit, 175km (110 miles) north of Baghdad
The militant leader arrested on Sunday was not named, but officials said he was a leader of a nationalist group known as the 1920 Revolution Brigades.
The announcement came a day after the Iraqi government said it had captured a leader of the radical Sunni Islamist group Ansar al-Sunna, which has been blamed for a number of suicide bombings, kidnappings and beheadings.
But the group, which is believed to have links to al-Qaeda, has denied any of its leaders were captured.