"We are outraged by this senseless act of violence against innocent civilians," State Department spokeswoman Jen Psaki told reporters, also condemning a series of attacks on three villages in Borno State over the weekend.
The bomb, which also injured 124 people, rocked the Nyanya station on Abuja's southern outskirts as it was filled with morning commuters, leaving body parts scattered across the terminal and destroying dozens of vehicles.
President Goodluck Jonathan blamed Boko Haram militants for the attack, but Psaki called for a "full investigation to identify and bring justice to the perpetrators of these attacks."
Washington was working with the Nigerian "government and its neighbors to address the growing threat of Boko Haram in a comprehensive manner," Psaki said, but warned it was too early to say the attack had been carried out by Boko Haram.
The United States designated Nigeria's radical Islamist Boko Haram network and an offshoot known as Ansaru as terror groups in November, bowing to months of pressure to act.
The State Department has offered a USD 7 million reward for information leading to the arrest of Boko Haram leader Abubakar Shekau.