President Trump said Sunday he is not considering firing Special Counsel Robert Mueller in the wake of calls from some Republican allies to shut down the Mueller probe into Russian involvement in the 2016 over allegations of bias by FBI officials.

"No, I'm not," Mr. Trump told reporters upon his arrival back at the White House. Mr. Trump spent Saturday night at Camp David.

Mr. Trump's attorneys are embroiled in a fresh spat with Mueller, the former FBI director, over his team's reported acquisition of thousands of emails from Mr. Trump's transition team. Mr. Trump's legal team wrote in a letter Friday that the emails had been obtained inappropriately from a federal agency and called for Mueller to return the documents. A spokesman for Mueller said all documents related to the investigation had been obtained through normal means.

Mr. Trump said he was "quite sad" to see Mueller had obtained the emails but doesn't think they contain any incriminating information.

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"My people were very upset about it," Mr. Trump said. "I can't imagine there's anything on them, frankly."

He added that there was "no collusion whatsoever" between Trump campaign officials and Russian operatives.

Mueller's probe has ensnared two former top Trump aides, Michael Flynn and Paul Manafort. Flynn pleaded guilty to lying to the FBI earlier this month. Manafort was indicted by a federal grand jury in October on several charges related to his overseas business dealings. Flynn served as Mr. Trump's short-lived national security adviser at the beginning of his administration, and Manafort ran the Trump campaign for several months in the summer of 2016.