It was not immediately clear if there were any US troops in the convoy or if anyone had been injured in the explosion, which went off just before 9 pm Baghdad time (1800 GMT), sources say.
Vehicles are regularly loaded with military equipment at the crossing, three Iraqi sources told Reuters.
The cargo is usually loaded or unloaded before entering or exiting Iraq, the sources added.
Foreign companies are contracted US forces to provide security in the area, the Iraqi sources said.
“We are currently looking into this matter,” said a spokesperson for the US Embassy in Kuwait.
A little known Iraqi group named Ashab al-Kahf claimed responsibility for the attack and published a video showing an explosion at a distance. It said it was able to destroy US military equipment and large parts of the crossing.