The bomb was detonated by remote control, injuring four soldiers in addition to the one who died, an Iraqi Army spokesman said.
Local authorities imposed a curfew in the area and American troops launched a search for those responsible.
US soldiers confirmed that a young girl was involved in the attack, which took place near Youssifiyah, south of the capital, Baghdad.
The horrific bombing came as Prime Minister Nouri al Maliki flew to Mosul to take charge of a major offensive against al Qaeda.
The US military says the northern city is the terror group’s last major urban stronghold in Iraq.
Military officials hope the offensive will deliver a knockout blow.
Sunni Islamist al Qaeda gunmen have regrouped in Mosul and the surrounding province of Nineveh after being pushed out of Baghdad and western Anbar province by US and Iraqi forces.
Moqtada al Sadr’s opposition movement struck a deal the ruling Shi’ite alliance to end running battles in Baghdad, although sporadic clashes keep breaking out.