Washington, Aug 15 (IANS): White House Press Secretary Sarah Huckabee Sanders said on Tuesday that she could not "guarantee" that US President Donald Trump had never used the word "nigger" to refer to blacks, after the accusation of an African American former adviser who said that she has tapes proving that he said it.

Sanders noted at her daily press briefing that Trump has specifically denied using the term on Twitter adding that "I can certainly say I've never heard him use that term or anything similar".

Sanders said, however, that she "can't guarantee" that the President had never used the pejorative term since she had not been at every working meeting he had ever held in the White House, Efe reported.

The White House spokesman was responding to the accusations of Omarosa Manigault-Newman, the former Trump advisor on African American issues, who said that she has audiotapes on which the president uses the term "nigger", considered taboo in the US because of its demeaning and heavily racist tone, not to mention its links with slavery.

Sanders said that Manigault-Newman's comments were regrettable and charged her with a lack of "integrity" for - by her own admission - having secretly taped conversations with the president and other top administration officials.

Trump, meanwhile, in a Twitter message on Tuesday morning responding to Manigault-Newman's remarks, said: "When you give a crazed, crying lowlife a break, and give her a job at the White House, I guess it just didn't work out. Good work by General Kelly for quickly firing that dog!"

Referring to the harshness of those insults, Sanders said that the president was expressing "his frustration" with the ex-adviser.

After in 2004 participating as a contestant in "The Apprentice" and other television reality shows hosted by Trump on NBC, Manigault-Newman became one of the mogul's confidants, and one he did not hesitate to hire for his White House team when he became president in January 2017.

Manigault-Newman held the post of communications director in the White House public liaison office until last December, when she resigned for reasons that were never clarified.

This week, however, the ex-adviser will publish her tell-all memoir "Unhinged" in which she discusses her time on the inside of the Trump administration.