Image copyright AP Image caption "We sit there [at the State of the Union address] as stone-faced, sober judges. But we're not," Justice Ginsburg admitted to an audience

US Supreme Court Justice Ruth Bader Ginsburg has admitted there is a reason she was seen nodding off at the president's State of the Union address.

"I wasn't 100% sober," she said at an event with fellow Justice Antonin Scalia.

She said she "couldn't resist the fine wine" at the dinner which traditionally brings together some of the court's justices before the speech.

At 81, Justice Ginsburg is the oldest serving judge on the Supreme Court.

She was asked about the incident by the moderator at an event at George Washington University on Thursday evening.

Justice Ginsburg was repeatedly pictured slumbering in her chair as President Barack Obama addressed the joint session of Congress in the House of Representatives on 20 January.

"The audience for the most part is awake, but they're bobbing up and down all the time. And we sit there as stone-faced, sober judges. But we're not.

Image copyright AP Image caption At 81, Justice Ginsburg is the oldest serving judge on the Supreme Court

"At least I wasn't 100% sober when we went to the State of the Union," she said, provoking audience laughter.

Justice Ginsburg said she had vowed to stick to sparkling water after dozing at the speech in past years, but was unable to resist the lure of a "very fine California wine" brought by Justice Anthony Kennedy.

"In the end, the dinner was so delicious it needed wine," she said.

"Well, that's the first intelligent thing you've done," quipped Justice Scalia.

Former Justice David Souter used to give her a pinch when he spotted the warning signs in years gone by, Justice Ginsburg said, but the judges beside her this time were "more timid".