Facebook has apologised after its content-filtering algorithms flagged the US Declaration of Independence as a hate speech.

Parts of the document was flagged as "hate speech" by Facebook bots after a Liberty, Texas-based newspaper, the Liberty County Vindicator, posted on Facebook "small bites" from the Declaration in the lead up to the country's Independence Day on July 4.

Facebook later restored the post and tendered an apology to the newspaper, Liberty County Vindicator said in a report on Tuesday.

The newspaper broke the Declaration down into 12 small bites and decided to post one each morning from June 24 to July 4.

The first nine parts posted as scheduled, but The Vindicator found that part 10, consisting of paragraphs 27-31 of the Declaration, did not appear.

Instead, it received a notice from Facebook saying that the post "goes against our standards on hate speech."

While The Vindicator said it could not be certain exactly what triggered Facebook's filtering program, the editor suspected it was most likely the phrase "Indian Savages", the newspaper said.

However, Facebook realised its mistake and restored the post after The Vindicator raised an alarm.

"It looks like we made a mistake and removed something you posted on Facebook that didn't go against our Community Standards. We want to apologise and let you know that we've restored your content and removed any blocks on your account related to this incorrect action," Facebook was quoted as saying in a statement sent to The Vindicator.