The bus was heading from Mandalay, near the Iranian border, towards the provincial seat of Baquba when gunmen stopped it and shot dead seven of its passengers.
Police also reported that a police lieutenant was shot dead in Baquba city itself.
Southeast of the capital, in the central city of Kut, gunmen attacked an Iraqi army patrol, killing two soldiers.
In Baghdad, a late night raid by US soldiers on Monday resulted in clashes with Shia militias, with police reporting at least six civilians killed.
In central Baghdad, gunmen wearing Iraqi police commando uniforms kidnapped as many as 100 men from a Higher Education Ministry building on Tuesday, a spokeswoman for the ministry said.
She said gunmen arrived in new pick-up vehicles and stormed the ministry's Research Directorate building in Karrada, a religiously mixed neighbourhood.
They ordered all the women into one room, took away their cellphones, and seized the men, who included employees, guards and visitors to the office.
An interior ministry source had earlier put the number kidnapped at around 20.
The Higher Education Minister is a member of the Iraqi Accordance Front, a Sunni group in the government.
The kidnapping recalled a mass abduction in July when gunmen seized around 30 people from an Iraqi Olympics Committee meeting in a brazen daytime raid in Baghdad. Six were later released.
On that occasion the kidnappers were wearing blue camouflage uniforms of the type used by the Interior Ministry.
Sportsmen and academics have been frequent targets of violence. Criminal gangs also kidnap people for ransom.

Copyright Reuters, 2006

Copyright AFP (Agence France-Presse), 2006