Former FBI director James Comey, who was abruptly fired by US President Donald Trump in May, revealed himself on Monday to be the owner of a mysterious Twitter account.

Speculation had been rife for months that Comey was behind the account named after 20th century American theologian Reinhold Niebuhr.

Comey confirmed it on Monday by tweeting a picture of himself standing on a road staring into the distance.

The picture was accompanied by a tweet which said: "Goodbye Iowa. On the road home. Gotta get back to writing. Will try to tweet in useful ways."

In another tweet, Comey posted a picture of the Civil War battlefield at Gettysburg, Pennsylvania, and mused: "Good place to think about leadership and values."

That Comey was behind the account was originally posited earlier this year by technology website Gizmodo, which cited a number of clues including the fact that Niebuhr was the subject of Comey's college undergraduate thesis.

The account originally had the handle @projectexile7 but has been renamed @FormerBu -- presumably for former bureau as in Federal Bureau of Investigation.

Comey has maintained a relatively low public profile since being dismissed as FBI chief, a move which came amid an FBI probe into whether any members of Trump's 2016 White House campaign colluded with Russia.

A special counsel has since been appointed to look into the allegations, which have been denied by the president.

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