Special Counsel Robert Mueller (R) departs after briefing members of the U.S. Senate on his investigation into potential collusion between Russia and the Trump campaign on Capitol Hill in Washington, U.S., June 21, 2017. REUTERS/Joshua Roberts

ABOARD AIR FORCE ONE (Reuters) - President Donald Trump is not moving to fire U.S. Special Counsel Robert Mueller but is frustrated by the length of the ongoing probe into Russian meddling in the 2016 U.S. election, the White House said on Monday.

Spokesman Hogan Gidley told reporters on the Air Force One flight carrying Trump to New Hampshire that Trump’s weekend tweets criticizing Mueller by name do not presage a firing.

“The president is not moving to get rid of Robert Mueller,” he said. He said the tweets reflected “some well-established frustration” felt by Trump over the Russian investigation.