US President Donald Trump wrote but never sent a letter to James Comey detailing his reasons for firing the then-FBI director, and the letter is now part of the ongoing investigation into the matter, US media reports.

Trump wanted Comey to publicly state the president was not under investigation in conjunction with a probe into Russian meddling in the US presidential election, the Wall Street Journal reported.

An official familiar with the letter paraphrased it as saying, “You’ve told me three times I’m not under investigation but you won’t tell the world, and it’s hampering the country.”

The letter was never sent but is now part of an independent counsel’s investigation that includes looking into potential obstruction of justice in Trump’s handling of the firing, the New York Times reported.

Comey oversaw the federal investigation of Russia’s alleged hacking of Democratic Party targets and other election-related intelligence operations, including possible links to the president’s campaign organistion, before being fired by Trump in May.

The White House provided conflicting explanations about why Trump fired Comey.

In closely watched testimony to Congress in June, Comey alleged that Trump had solicited a pledge of personal loyalty, pressed him repeatedly for reassurances that Trump was not under investigation and sought to have him end a probe into former national security advisor Michael Flynn.