"The booby-trapped motorbike exploded as the patrol passed by. Four soldiers were killed and their vehicle destroyed," captain Farid al-Tamimi said.
The attack took place behind the general hospital in al-Risala neighbourhood, in the centre of Basra, the country's second largest city on Saturday.
British forces sealed off the site after the blast.
Unrest in Samarra
Two children were also killed when a landmine exploded on Saturday in Samarra, north of Baghdad, security and medical sources said.
Two Iraqi soldiers were killed in a roadside bomb attack in the same city, which US-led troops raided in October in an effort against resistance fighters ahead of the landmark elections.
In further unrest in Samarra, another soldier and a civilian were killed during clashes between Iraqi security forces and fighters in the city centre, police lieutenant Husain Abbas said.
In nearby Dhuluiya, a soldier was killed and four civilians wounded in clashes, police captain Amjad Saad said.
US soldiers killed
Meanwhile, a roadside bomb blast killed two US soldiers and wounded five near the northern Iraqi town of Baiji on Friday, the US military said on Saturday.
Earlier in the day, another roadside bomb blast in the same area killed one American soldier and wounded seven.
Since the US-led invasion of Iraq in 2004, 1107 American soldiers have been killed in action. Including non-combat deaths, the toll is 1447.
Separately, four bodies of Iraqi police officers, who went missing a few days ago, were found in the Abu Ghraib area west of Baghdad, Iraqi police sources told Aljazeera.
Fourteen Iraqi police officers were announced missing several days ago after fighters attacked their convoy in the city of al-Diwaniya.
The Ansar al-Sunna group has claimed responsibility for capturing some of the missing officers.