An explosion hit a market area of Hussainiya in Baghdad's northern outskirts, killing four people. A second, in a street in eastern Baghdad, apparently targeting the convoy of an interior ministry official, killed one of his guards and a bystander.
The attacks followed a week of arrests in Baghdad by the Iraqi government of Sunni Arab fighters known as Awakening Councils, or Sahwa.
The Iraqi government insists it is only detaining those wanted for grave crimes, but the fighters - many of them former fighters - fear it is settling sectarian scores.
Kadhum al-Muqdadi, a Baghdad University professor, suggested the bombs might be an attack in response to the raids, one of which sparked clashes just over a week ago between Iraqi forces and supporters of an arrested Sahwa leader.
|An Iraqi police officer stands next to a bombed car at the site of an attack in Baghdad [AFP]
"Any security action carries the risk of a reaction," he said.
"These could be the work of Sahwas or just of opportunists exploiting this issue."
The Sahwas first switched sides and joined with US forces to fight al-Qaeda in Iraq in late 2006, manning checkpoints and conducting raids.
US officials have doubted claims that the Awakening Councils may have been behind Monday's bombings.
Lieutenant-Colonel Philip Smith, a military spokesman, said: "Our assessment is that the attacks today were a co-ordinated effort by al-Qaeda. There were no indicators that the [Sahwa fighters] ... were involved in any of the attacks."
Sheikh Hameed al-Hayyes, a founder of the Sahwa movement, also said the bombs were unlikely to be the work of the guards.
"There were bombings in Baghdad before the arrests and after the arrests," he said, blaming al-Qaeda in Iraq for the attacks.
Qassim al-Moussawi, a Baghdad security spokesman, said the attacks "carry the fingerprints of al-Qaeda-linked groups".
Iraqi and US officials say a small number of the 90,000-odd Sunni guards still have links to al-Qaeda and other fighter groups. But the government insists they are a minority.
"Al-Qaeda is trying to infiltrate the Sahwa, but I think it will not succeed, because the Sahwa have seen their crimes and brutality," Ali al-Dabbagh, the Iraqi government spokesman, said.
The latest attacks underscore the challenges Iraqi security forces face as US combat troops prepare to withdraw by August 31, 2010, with all US troops due to leave by the end of 2011.
Bombings continue on an almost daily basis in Iraq, despite the sharp fall in violence.
The last large bomb blast in Baghdad killed 20 people in a shopping district on March 26.
Preventing all car bombs in the crowded streets of Baghdad - a maze of crumbling buildings and concrete walls housing millions of people - is all but impossible.