Mr Sessions is likely to face questions by the SenateIntelligence Committee over his dealings with Russian officials during President Donald Trump's election campaign and whether he had a role in firing former FBI Director James Comey.
Sessions's testimony comes as the committee probes potential collusions between President Donald Trump's campaign team and an alleged Russian campaign aimed at skewing the 2016 presidential race in his favor.
Sessions is scheduled to testify at 2:30 p.m. on Tuesday.
"I think it depends on the scope of the questions", Spicer said.
Comey told the intelligence committee in a closed session that Sessions may have had a third, undisclosed interaction with Russia's ambassador to the USA, according to people familiar with the briefing.
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A third participant in that meeting, White House senior adviser and Trump's son-in-law Jared Kushner volunteered in March to testify before the intelligence committee. Officials said that Sessions at one point offered to resign as his relationship with the president became increasingly tense. Sessions, a former senator, later issued a clarification saying he had met with the ambassador.
Mr Trump had himself attributed his dismissal of Mr Comey to the Russian Federation investigation.
It comes as political intrigue pulses through the USA capital following explosive testimony by Comey before the same panel last week, and as Trump has expressed frustrations with Sessions, one of his earliest high-profile campaign backers.
Lawmakers, including Al Franken of Minnesota and Patrick Leahy of Vermont, have asked the FBI to investigate and to determine if Sessions committed perjury when he denied having had meetings with Russians.
Elizabeth Warren (D-MA), said Attorney General Jeff Sessions needed "to be fired".
Later, Comey said he was so uncomfortable that he went to Sessions to "implore" him "to prevent any future direct communication between the President and me".
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Comey said he could address the details only in a classified setting - heightening the suspense about what might be asked and answered on Tuesday.
Reed said he also wants to know if Sessions had more meetings with Russian officials as a Trump campaign adviser than have been disclosed.
Almost a month after firing off a suggestion on Twitter that such tapes may exist, Trump still refused to answer the question directly. And Sessions has sat through enough hearings to know his answers will come back to bite him if there is even an element of untruth. "The president then excused him, saying he wanted to speak with me".
"I don't think we finish those whole conversations until we just know everything, so I just want more information about everything that can come out", the IL lawmaker said.
White House spokesman Sean Spicer declined to discuss Trump's "private conversations" with Sessions about Comey, and he left open the possibility that the administration may ask the attorney general to invoke executive privilege regarding them.
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