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.

The-CNN-Wire

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