(CNN) Special Counsel Robert Mueller's office interviewed Deputy Attorney General Rod Rosenstein over the summer about his role in President Donald Trump's firing of former FBI Director James Comey, according to a person familiar with the matter.

The questioning by investigators of the top DOJ official overseeing the probe is a rare occurrence, but the source said that Rosenstein has no plans to immediately recuse himself, an indication Mueller's office does not view him as a key witness in the obstruction of justice probe.

Rosenstein wrote a memo detailing his concerns about Comey's handling of the Hillary Clinton email server investigation that the White House initially cited as the reason for firing Comey.

Ian Prior, a spokesman for the Justice Department, said in a statement, "As the deputy attorney general has said numerous times, if there comes a time when he needs to recuse, he will. However, nothing has changed."