Former FBI Director Robert Mueller, special counsel on the Russian investigation, leaves the US Capitol building following a meeting with members of the US Senate Judiciary Committee a on June 21, 2017.
SAUL LOEB/AFP/Getty Images
Former FBI Director Robert Mueller, special counsel on the Russian investigation, leaves the US Capitol building following a meeting with members of the US Senate Judiciary Committee a on June 21, 2017.
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WASHINGTON, DC - JUNE 21:  Special counsel Robert Mueller (2nd L) leaves after a closed meeting with members of the Senate Judiciary Committee June 21, 2017 at the Capitol in Washington, DC. The committee meets with Mueller to discuss the firing of former FBI Director James Comey.  (Photo by Alex Wong/Getty Images)
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WASHINGTON, DC - JUNE 21: Special counsel Robert Mueller (2nd L) leaves after a closed meeting with members of the Senate Judiciary Committee June 21, 2017 at the Capitol in Washington, DC. The committee meets with Mueller to discuss the firing of former FBI Director James Comey. (Photo by Alex Wong/Getty Images)
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US President Donald Trump (L) chats with Russia's President Vladimir Putin as they attend the APEC Economic Leaders' Meeting, part of the Asia-Pacific Economic Cooperation (APEC) leaders' summit in the central Vietnamese city of Danang on November 11, 2017. / AFP PHOTO / SPUTNIK / Mikhail KLIMENTYEV (Photo credit should read MIKHAIL KLIMENTYEV/AFP/Getty Images)
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Special counsel investigators could start interviewing current and former White House staff as soon as later this week regarding the Russian probe, two sources familiar with the matter tell CNN.

One source cautioned it is still being worked out with Robert Mueller’s office and said it might be delayed until next week.

As CNN previously reported, among the people Mueller has expressed interest in speaking with are former and current White House staffers whom investigators consider witnesses, including former chief of staff Reince Priebus, former press secretary Sean Spicer, communications director Hope Hicks, White House counsel Don McGahn, communications adviser Josh Raffel and associate counsel James Burnham.

Mueller’s team also approached the White House about interviewing staffers who were aboard Air Force One for the creation of the initial response to news of Donald Trump Jr.’s Trump Tower meeting with a Russian lawyer, sources previously told CNN.

Mueller’s investigators are looking for documents and emails relating to the dismissals of national security adviser Michael Flynn and FBI Director James Comey, according to the sources. In addition, one source confirms that Mueller’s team wants information connected to the Oval Office meeting Trump had with Russian officials in which he bragged about firing Comey, saying it eased pressure on his White House.

The special counsel’s office declined to comment.