Secretary of State Mike Pompeo says the US welcomes an immediate investigation into any use of excessive force.
The United States on Thursday condemned what it called excessive use of force by the Nigerian military for firing on unarmed demonstrators.
Amnesty International says at least 12 people were killed by the Nigerian army and police in a brutal crackdown on protesters Tuesday that drew international condemnation.
"We welcome an immediate investigation into any use of excessive force by members of the security forces," Secretary of State Mike Pompeo said in a statement.
Nigeria's army has dubbed as "fake news" reports that soldiers opened fire on demonstrators.
Police Minister Muhammad Maigari Dingyadi told the BBC that troops were not ordered to open fire on protesters.
Pompeo said that those involved "should be held to account in accordance with Nigerian law."
"The right to peaceful assembly and freedom of expression are essential human rights and core democratic principles," Pompeo said.