A US citizen was one of at least 55 people killed in Tuesday's blast near a Shiite shrine in the Afghan capital Kabul, the US embassy in the city said Wednesday.
"Yes, that's true. I can't comment further on that pending the family's instructions," said embassy spokeswoman Megan Ellis.
The embassy added that its staff were in contact with the dead person's family and were "providing all appropriate consular assistance".
The blast happened as Shiite Muslims marked the holy day of Ashura, ripping through a crowd of worshippers and leaving a devastating aftermath.
The Afghan Taliban have denied responsibility for the attack.
There are around 140,000 foreign troops fighting in Afghanistan, some 100,000 of them from the United States. Around 30,000 US troops are due to have returned home by September 2012.