"We can confirm there was one fatality and four injured," British army spokesman Major Steve Melbourne said.
The blast on Sunday hit an armoured four-wheel-drive vehicle in the northern district of Maakal, sending it crashing into a wall, according to pictures taken at the scene.
In London, the Ministry of Defence confirmed the incident and said it was under investigation.
Ninety-eight British soldiers have been killed in Iraq, including 65 in hostile action, since the US-led invasion in March 2003, according to an AFP toll.
An ambush on a joint US-Iraqi patrol northeast of Baghdad left 15 civilians, eight fighters and a US marine dead from a roadside bomb and the firefight that followed.
The attack began with the bomb detonating next to the marine's vehicle in the town of Haditha, 220km northwest of Baghdad, on Saturday, the US command said on Sunday.
A British soldier was killed in a
roadside bomb attack in Basra
Fifteen civilians were killed by the blast, which was followed by an attack with small arms, the statement said.
"Iraqi army soldiers and marines returned fire, killing eight insurgents and wounding another," the statement added.
Aljazeera reported sources in the town saying US forces bombed four houses and killed 31 Iraqis, leaving bodies in the streets.
At least 2091 members of the US military have died since the war began in March 2003, according to an Associated Press count.
A former member of the Baath Party was killed by armed men in the city of Karbala, 110km southwest of Baghdad, police say. His 14-year-old son was also killed in the attack.
Two members of the Iraqi Islamic party in Buhriz, 60km northeast Baghdad, were found in a Baghdad morgue. They had been shot dead. Relatives of the victims said they were taken by Interior Ministry commandos about a week ago.
In the capital, three Iraqi soldiers were killed and five wounded by a makeshift bomb, police said.
A US soldier was killed in
Baghdad by small-arms fire
A US soldier was also killed in Baghdad on Sunday by small-arms fire during a patrol north of the city.
In Baquba, 19 Iraqis were killed by a bomber driving a booby-trapped car.
One man was seriously wounded in a mortar attack on a US military base north of the city of Hilla, 100km south of Baghdad, police said.
Mosul gun battle
In Mosul, 362km northwest of Baghdad, Iraqi officials said police and US soldiers surrounded a house before dawn on Saturday after reports that al-Qaida members were inside, said Brigadier Said Ahmad al-Juburi, a Mosul police spokesman.
As a fierce gun battle broke out, three fighters detonated explosives and killed themselves to avoid capture.
Five more died fighting, while four police officers were killed.