Aljazeera has learned that in addition to the fatalities in Karbala, a women and her child were injured in Sunday's incident, which involved an explosion in a house in the western al-Askari suburb.
A police source said the blast was most likely caused by an explosive device blowing up while being prepared for a sabotage operation.
In Baghdad, politician Abd al-Husain of the Democratic Party of the Iraqi Nation died instantly when three masked armed men opened fire as he left his home on Sunday, party leader Mithal Alussi said.
He blamed the Baath party of ousted president Saddam Hussein and intelligence agents of neighbouring Syria for the killing.
The Democratic Party of the Iraqi Nation was recently expelled from a wider coalition after Alussi made a trip to Israel.
Also on Sunday, a civil defence colonel and an aide were killed when an armed group opened fire outside the officer's home in southwestern Baghdad, police said.
In another incident, three US soldiers were wounded in a bomb attack on their patrol in Mosul, just days after an attack killed 22 people at a US base in the main northern city.
A civil defence colonel and an
aide were shot in Baghdad
North of the capital, an Iraqi National Guard member was killed and a civilian wounded when a makeshift bomb exploded as a convoy passed on the road between Samarra and Dhuluiya, security sources said.
Further north, a father and son were killed in a roadside bombing in the refinery town of Baiji, police said.
A Turkish truck driver was also killed by armed men as he passed through the town.
In other incidents, a local official was seized overnight in the town of Shurgat near Mosul, police said.
"Muhsin al-Sabhan was kidnapped in the night by gunmen with two of his bodyguards, who were released two hours later," Colonel Abd Allah Jaburi said.
Meanwhile, residents of al-Andalus suburb of Falluja have buried 150 bodies in the Martyrs' Cemetery in the centre of the town.
The bodies, found under the rubble of destroyed buildings, were mostly of children, women and elderly whose identity were established by returning Falluja residents.
The search is continuing for other Fallujans presumed dead.