Conflicting reports have emerged over whether Beyonce sang live at President Barack Obama's inauguration.
A spokeswoman for the Marine Corp Band told The Times in a "last minute" decision, Beyonce opted to perform to a pre-recorded backing track.
However, the Marine Corp told the BBC "no-one in the Marine Band is in a position to assess whether it was live or pre-recorded".
But it confirmed that the band itself was not playing live.
Millions of people tuned in to watch the president be sworn in for his second term in office. The ceremony was punctuated by performances from James Taylor, Kelly Clarkson, as well as Beyonce, who sang the national anthem.
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When The Times reported that the singer had mimed, the story quickly travelled around the world.
The newspaper quoted a spokeswoman for the Marine Corp Band, Master Sergeant Kristin duBois, who said: "We pre-recorded all music as a matter of course and have done since time immemorial.
"This is our 54th inauguration… There is no question of there not being any music, it's not because the performer cannot do it."
However, the spokeswoman did not state outright that Beyonce mimed her part of the performance.
In a statement, the Marine Corp gave the BBC a fuller picture of the events: "There was no opportunity for Ms Knowles-Carter to rehearse with the Marine Band before the inauguration so it was determined that a live performance by the band was ill-advised for such a high-profile event.
"Each piece of music scheduled for performance in the Inauguration is pre-recorded for use in case of freezing temperatures, equipment failure, or extenuating circumstances.
"Regarding Ms Knowles-Carter's vocal performance, no one in the Marine Band is in a position to assess whether it was live or pre-recorded."
Some reports suggested the singer had pre-recorded her vocal in a studio at the Marine Barracks Annex on Sunday night.
They were drawing inferences from a series of images posted on the star's website over the weekend - one of which showed her in the studio holding the sheet music for the Star Spangled Banner.
If the claims turned out to be true, they would not be without precedent.
In 2008, American cellist Yo Yo Ma mimed his performance at President Obama's first inauguration, saying the freezing temperatures and wind might have affected his instrument live.
Celebrities and fans have been debating Beyonce's performance on Twitter.
TV presenter Piers Morgan said: "Beyonce still SANG it, everyone. It was HER voice."
Brooklyn band Prince Rama commented: "I actually think Beyonce lip-syncing the national anthem is one of the best conceptual art pieces I've seen in a long time."
While Los Angeles musician Michael Anthony said: "It doesn't even look like Beyonce was lip syncing at all."
A blog post on the Washington Times website said: "Some Beyonce fans insist it looked real, especially when she ripped out her earpiece midway through the song".
The BBC contacted Beyonce's representatives for comment but had not received a response at the time of writing.