The blast occurred in al-Mafriq area of central Baquba, Aljazeera's correspondent reported on Monday.
The injured have been transferred to hospitals in Baghdad.
Meanwhile, two blasts rang out over central Baghdad in the early hours of Monday and smoke rose from the heavily fortified Green Zone housing the US-led occupation authorities' headquarters.
Sirens could be heard from the zone shortly after the blasts and two helicopters flew near the plumes of smoke.
There was no immediate word on the cause of the explosions.
Attacks on the Green Zone have become an almost daily occurrence by those resisting the US-led occupation of Iraq. On Sunday morning, up to seven explosions were heard from inside the area.
US soldiers killed
Also on Monday, the US military announced that one US soldier was killed and four were wounded when their patrol was attacked near Samarra, north of the capital Baghdad.
The statement said the soldiers from the 1st Infantry Division came under attack at about 4:35 p.m. (1235 GMT) on Sunday. The wounded were in stable condition.
Also, a military support convoy with a cargo of armoured personnel carriers was attacked and burned on a road in Latifiya 35km south of the Iraqi capital Baghdad on Monday.
Several of the flat bed trucks in the convoy were carrying M113 military vehicles. Witnesses said that eight trucks had been attacked and three people were dead.
It is not known how any people were injured or if any were taken hostage during the attack.
An Iraqi man checks the attacked
military support convoy
Meanwhile, it was announced on Monday that one Romanian civilian security worker was killed and another one injured on Sunday in an ambush near Baghdad, Romania's Foreign Ministry said.
The injured worker underwent surgery in a hospital in the Iraqi capital and is now out of danger, the ministry said in a statement.
The workers were employees of a private security company
working in Iraq but did not release the firm's name, it added.
"Several cars full of employees of a security company came
under fire Sunday afternoon," Romanian ambassador to Iraq Mihai Stuparu told a private Romanian television station.
Kut curfewUS forces have imposed a curfew upon the town of Kut, south of Baghdad, affecting not only civilians, but the Iraqi police too. The curfew is effective from 22:00 to 06:00 GMT, Aljazeera's correspondent reported.
Ten residents were earlier arrested during US search operations in different areas of the town, the correspondent said.
Ukrainian troops have also returned to Kut, the correspondent added.
On Sunday, three US Marines were killed "in combat" west of Baghdad, the occupation army said.
The three, members of the 1st Marine Expeditionary Force, were killed in al-Anbar province, which stretches from the west of Baghdad to the Jordanian and Syrian borders.
The army did not identify the three and gave no other details.
At least 664 US soldiers have died in Iraq since the war began in March 2003.
In other developments:
- A German aid organisation is due on to fly its last foreign workers out of Iraq because of the increasing risk of attack, its head said.
- US officials are seeking a truce with Shia leader Muqtada al-Sadr, an official of the Supreme Council for Islamic Revolution in Iraq said in Iran, adding it was acting as a go-between.
- US aircraft dropped leaflets on Karbala telling people to stay away from occupation bases and warning them that troops will retaliate if attacked.