The US Embassy in Suva is investigating last week's deportation of a woman from Fiji to Los Angeles over allegations she swore at the President Jioji Konrote.
Karen Seaton, who also has Canadian citizenship, was deported just hours after protesting against land laws at parliament.
Fiji's government said she breached the terms of her residency permit by using the 'F' word against Mr Konrote, but Ms Seaton denies swearing at the President.
The Embassy's Regional Public Affairs Officer, Dmitri Tarakhovsky, said they are looking into the incident.
"The embassy takes support of US citizens very seriously. We are looking into accounts that a US citizen was reportedly detained and deported and are seeking additional information from the Fijian government. Due to privacy considerations, we have no further information at this point."
Karen Seaton holds US, Canadian and British passports.
Fiji's Law Society said immigration laws allow for a person to be deported if they insult someone.
It said the Minister has the power to declare a person a prohibited immigrant under the Immigration Act if the person is deemed to be a person who is or has been conducting themselves in a manner prejudicial to the peace, defence, public safety, public order, public morality, public health, security or good government of Fiji.
It said it is also an offence under the Crimes Decree to indecently insult or annoy any person.