The bomb went off just after 9am (local time) on Wednesday but no soldiers were injured, US military spokeswoman Captain Kelly Lewis said.
Iraqi police Captain Talib Thamir added that the bomber, who died in the blast, was targeting a checkpoint that is mainly manned by private security guards backed by US troops.
A security official at western Baghdad's main Yarmouk Hospital said earlier that three Iraqi Airways employees were wounded.
One of the victims, Ghassan Yassin, said he suffered facial wounds as a result of the blast.
The bomber targeted a checkpost
mainly manned by private guards
"Me and some colleagues at Iraqi Airways were waiting in line when we saw a speeding car, then we heard a big explosion," Yassin said. "The next thing I realised is that my car was on fire. I got out through the window after the doors jammed due to the explosion."
Baghdad International has often come under mortar attack, and vehicles travelling on the road leading to it from downtown Baghdad are routinely targeted by bombs.
In an unrelated development, an Iraqi soldier died from poisoning and nine others were in critical condition after they ate free watermelon handed out at a checkpoint in northern Iraq, police said on Wednesday.
"A vendor offered a poisoned watermelon on Monday to Iraqi soldiers manning checkpoints between Shorgat and Kiyara," said police Colonel Fares Mahdi.
"One soldier died and nine others who were rushed to the hospital are in critical condition."
Police were searching for the assassin in what is thought to be the first such attack against Iraqi security forces.