(CNN) Special counsel investigators interviewed former White House press secretary Sean Spicer on Monday as part of the Russia investigation, a source familiar with the matter told CNN.

Spicer is the third White House-related official to be interviewed by Robert Meuller's investigators in the past few weeks. Last week, former Chief of Staff Reince Priebus was interviewed and investigators recently interviewed Keith Kellogg, executive secretary of National Security Council.

CNN was told by a separate source last week that there is an expectation that Mueller's team will wrap up interviewing the first group of White House officials by the end of the month.

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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 Priebus, Spicer, communications director Hope Hicks, White House counsel Don McGahn, communications adviser Josh Raffel and associate counsel James Burnham.

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