"One soldier has died and two have been wounded as a result of an IED attack near Baquba on Wednesday," the officer told AFP on Thursday.
A convoy was hit by a roadside bomb west of Baquba and three soldiers were injured, with one of them dying later in hospital, he said.
It was the second such fatal explosion in that area in 24 hours.
Added to an official Pentagon tally, the pair of deaths since Tuesday raises to 266 the number of US soldiers killed in action since US President George Bush declared official hostilities over on 1 May.
A bomb exploded on Wednesday outside the office of one of the main Shia parties in the Iraqi town of Baquba, injuring at least one person and badly damaging the building, police and witnesses said.
The blast just after 6am (03:00 GMT) on Wednesday shattered windows and doors at the offices of the Supreme Council for the Islamic Revolution in Iraq (SCIRI), in Baquba, north of the capital.
"They will be transported to a prison in Baghdad and interrogated by American troops because the victims are of American nationality"
Colonel Robert Strzelecki,
Spokesman, Polish military
Shia leaders, including the head of SCIRI, have criticised a transitional constitution signed on Monday, and raised concerns about certain clauses that they feel could jeopardise their representation.
Meanwhile, scattered explosions and small-arms fire were heard on Wednesday morning in central Baghdad, while a mortar round fired by US soldiers in northern Iraq missed its target earlier this week, killing an Iraqi civilian, the military said.
A US military spokesman could not confirm the cause of the blasts in Baghdad, but said they might have been controlled bursts to destroy captured stockpiles of ammunition and ordnance.
Two Americans working for the US-led occupation authorities were shot dead, along with their Iraqi translator, after their car was stopped at a makeshift checkpoint in south-central Iraq by men dressed as Iraqi policemen, a Polish military spokesman said on Wednesday.
The shooting occurred outside Hillah on Tuesday night, Colonel Robert Strzelecki said by telephone from the Camp Babylon headquarters of the Polish-led multinational force in Iraq.
Polish troops arrested five Iraqis during the night and found the victims' bodies in their car, he said.
The assailants were detained.
"They will be transported to a prison in Baghdad and interrogated by American troops because the victims are of American nationality." Strzelecki gave no information on the victims' identity.
Ansar al-Islam arrest
Explosions and attacks continue
to occur throughout Iraq
Aljazeera's correspondent in Baghdad reported that US occupation forces on Wednesday arrested a leading member of Ansar al-Islam group, which the occupation authorities have accused of being behind several bombings in Iraq and of cooperating with al-Qaida network.
Kamiran Arbili, known as Ayub al-Afghani, was detained in Baghdad and not in Kirkuk.
Arbili is a senior security official.
In northern Iraq, the 3rd Brigade 2nd Infantry Division fired the mortar round as part of a strike against insurgents on Monday, when it fell short and hit a building on the south-east side of Ijba, near Mosul, about 365km north-west of Baghdad.
One Iraqi civilian was killed and another wounded, the military said on Wednesday.
The strike is under investigation.
Aljazeera's correspondent in Iraq reported that a rocket attack on Wednesday targeted a US military vehicle in the al-Mashahda area, north of Baghdad, setting it ablaze.
The correspondent adds that US forces, using helicopters then attacked a civilian Iraqi car. The car was damaged, but the occupants were not hurt.
Iraq Body Count, an independent database, estimates the civilian death toll at between 8400 and 10,300 people killed as a direct result of the war and subsequent occupation.