The US Marine Corps beat a hasty retreat Tuesday from a furor over whether Beyonce lip-synched "The Star-Spangled Banner" at President Barack Obama's public inauguration ceremony.

First, the New York Times quoted a US Marine Band spokeswoman as saying that, just before Beyonce took the stage Monday, the musicians learned a version of the national anthem it had pre-recorded with her would be used.

"We don't know why," said the spokeswoman, Master Sergeant Kristin duBois. "But that is what we were instructed to do... It's not because Beyonce can't sing. We all know Beyonce can sing. We all know the Marine Band can play."

But later, the Marine Corps said only that a pre-recorded version of the band's musical track was played to the crowd outside the Capitol after Obama was sworn into office for a second term.

Since the band did not have a chance to rehearse with Beyonce beforehand, "it was determined that a live performance by the band was ill-advised for such a high-profile event," it said.

But as for Beyonce's vocal performance, it added: "No one in the Marine Band is in a position to assess whether it was live or pre-recorded."

Beyonce's publicist did not respond to emails Tuesday, leaving it unclear as to whether or not the R&B diva had pulled off the biggest karaoke number in the history of US presidential inaugurations, or somehow just mimed the words.

Also unexplained was a black-and-white Instagram photo, supposedly taken Sunday, of Beyonce in a wool beret and cardigan in a recording studio with three soldiers behind her. She appeared to be listening intently to something.

Equally mysterious was why Beyonce removed the ear monitor mid-way through the song. Singers performing over an instrumental track might do so if the playback is clashing with what's coming out of the loudspeakers.

One way or another, fans of Beyonce -- who sang "The Star-Spangled Banner" live at last year's Super Bowl and returns to the American football classic in February as its half-time act -- rallied behind her on Twitter.

"Who cares that Beyonce Lip #Sync the National Anthem, it was recorded live an hour before. You try singing in that cold," tweeted one fan, referring to Monday's near-freezing temperatures in Washington.

"Beyonce certainly acted like a diva ... but I don't see how that can be compared to Lance Armstrong cheating for 7 straight years at the least," said another Twitter user, referring to the disgraced cyclist.

"Beyonce is the best lip-syncer I've seen," added a third fan. "Because she surely fooled me."

The US Marine Band is the premier musical ensemble of the US Marine Corps. It's also known as the President's Own for its longstanding connection with the White House and important national events.

It played live for most of Monday's inauguration on the Capitol steps, but prior to any major event, it routinely goes into the studio to record its repertoire as a precautionary measure.

"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," the Marine Corps statement said.

Pop star Kelly Clarkson and folk singer James Taylor also performed at the inauguration.