The Justice Department has notified Senate investigators that it will not make FBI officials available for interviews because doing so could pose conflicts with the work of special counsel Robert Mueller.
Leaders of the Senate Judiciary Committee had sought to meet with the FBI's chief of staff, James Rybicki, and the executive assistant director of its national security branch, Carl Ghattas, as part of their review into the dismissal of then-FBI Director James Comey earlier this year.
But the Justice Department told lawmakers this week that it would decline to make the FBI officials available "to protect the integrity of the special counsel's investigation."
Mueller is examining Russian interference in last year's presidential election and potential ties between the Trump campaign and Russians.
The special counsel probe also extends into "any matters that arose or may arise directly from the investigation." Sources familiar with the probe have told NPR that includes whether Comey was fired for any improper reasons, such as obstruction of justice.
A spokesman for Mueller declined comment for this story.
Legal experts who follow Washington scandals said it's common for prosecutors to prioritize witnesses needed for criminal investigations over congressional requests. But those decisions can produce friction with lawmakers on Capitol Hill.