The attack came as US Secretary of State, Condoleezza Rice, and her British counterpart, Jack Straw, concluded a surprise visit to Iraq warning against further delays in the formation of an Iraqi government.
The latest blast was set off near al-Shuruqi mosque in the al-Shaab neighbourhood, northeast of Baghdad.
The attacker drove his pickup truck loaded with explosives straight at the entrance of the mosque as worshippers were leaving.
The truck struck a concrete barrier surrounding the building and detonated, according to an interior ministry official.
A few hours earlier, the two diplomats ended their Iraq trip after urging political leaders to overcome differences and choose a strong figure to restore stability in a country that has edged to the brink of civil war more than three months after elections.
Deadlock continues
However despite the visit, acknowledged by officials as a high-stakes gamble to end weeks of political deadlock, there is still no sign of a breakthrough between Iraq's bickering factions.
"We came here to give momentum to the process that is already underway. It is not my responsibility or of Mr Straw to determine who is going to be the prime minister of Iraq," Ms Rice told a press conference at the end of their visit.
"That will be determined by Iraqis. But we need a strong, unifying government led by someone who can bring stability and meet the challenges of Iraqi people," she said.
Their visit in the midst of a political vacuum brought on by the lack of a new government came as the dominant conservative Shiite coalition asked US leaders to stop meddling in Iraqi affairs.
But Ms Rice warned "You cannot have a circumstance where there is a political vacuum in a country like this that faces so much threat of violence."
Mr Straw bluntly commented there was growing impatience in the United States and Britain which he said had sacrificed soldiers' lives and resources in building a new Iraq since their March 2003 invasion which ousted Saddam Hussein.
"We recognise that coalition building always takes time. But this is now taking more than that," he said.
Both envoys praised Grand Ayatollah Ali al-Sistani, the spiritual leader for much of the country's majority Shiite community, for his aid in building a new Iraq, suggesting he could help break the political deadlock.