Washington (CNN) White House chief of staff John Kelly has warned President Donald Trump to be careful about talking to witnesses in the Russia investigation, a White House official told CNN on Thursday.

When asked about a New York Times report that Trump has spoken with former chief of staff Reince Priebus and White House counsel Don McGahn about special counsel Robert Mueller's probe, a White House official said: "It's pretty clear that Kelly admonishes him constantly and he's not the only one."

This official described the President's discussion with Priebus as appropriate.

"There's nothing wrong with talking someone and saying, 'Did they treat you well?' " the official said.

But this official made it clear that the President's conversations about the investigation are making top aides inside the White House uncomfortable and potentially putting Trump himself in a legally precarious position.

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