A US aid worker was among four people killed during an ambush on their convoy in western Baghdad.
At least 15 people were killed in a car bomb attack in Sadr City
An American woman working for the National Democratic Institute died when gunmen attacked the three-car convoy, the US-based aid organisation said.
Security contractors from Croatia, Hungary and Iraq were also killed.
It comes after more than 20 people, including two US soldiers, were killed and dozens injured in separate bomb attacks in Iraq.
Two others were injured in the attack which occurred at midday Baghdad time, as the group was returning from a meeting in the Iraqi capital.
They had been at the headquarters of the Islamic Party, Iraq's leading Sunni Arab political bloc, in the Yarmuk district of Baghdad, two sources reported.
"It appeared to be an attack with fairly heavy weapons. We have information that a firefight ensued. Our security company responded to the attack," said Les Campbell, the group's Middle East director.
The Croatian, Hungarian and Iraqi were guards working for an Australian security agency, Mr Campbell said.
The National Democratic Institute (NDI) is a non-governmental organisation that provides support for political parties in Iraq.
President Kenneth Wollack said NDI personnel in Iraq were dedicated to helping improve the lives of citizens there.
"This is a tragic loss for the Institute and its Iraqi friends," he said.