Sunderland have apologised to their fans for the error at the Stadium of Light. Photo by MI News/NurPhoto via Getty Images

Sunderland's efforts to make Newcastle United supporters feel welcome for Saturday's FA Cup match hit a sour note with home fans after the club plastered their fierce rivals' slogans all over a bar at the Stadium of Light.

Sunderland owner Kyril Louis-Dreyfus apologised after images posted on social media showed signage at the Black Cats Bar, which is used by away fans, proclaiming "WE ARE UNITED" and "KEEP THE BLACK AND WHITE FLYING HIGH."

Newcastle traditionally play in black and white stripes while Sunderland play in red and white.

- Stream LIVE: Sunderland vs. Newcastle, FA Cup third round, Saturday, 7:30 a.m. ET, ESPN+

"I would like to apologise to everyone associated with Sunderland AFC for the events that have unfolded today," Louis-Dreyfus wrote on Instagram on Thursday.

"Like our supporters I was disgusted and hurt by the pictures circulating online of the inappropriate signs that have now been ripped down."

The cities of Sunderland and Newcastle in the northeast England are separated by just 12 miles and their football teams have a long-standing rivalry which has been marred by violence and crowd trouble in the past.

The pair have not met since March 2016, with Sunderland now in the second-tier Championship after being relegated in 2017, and Saturday's Tyne-Wear derby takes on added significance with the two sides matched on 53 wins apiece.

Sunderland acknowledged "a serious error in judgement" and said the club's ownership group and board of directors had requested an immediate review "to determine how this process unfolded."

While home fans were livid, Newcastle supporters welcomed the decor changes, with a supporters group posting on social media that they could not "fault the hospitality" of their hosts.