US President Donald Trump set off a barrage of early Sunday morning tweets directed at “slippery” James Comey ahead of the former FBI chief’s highly anticipated TV interview on Sunday (April 15) evening.

Calling Comey the “worst FBI director in history” Trump challenged accusations Comey makes in a tell-all book that is due for release this week and insisting that he never pressed Comey to be loyal to him.

“I hardly even knew this guy. Just another of his many lies. His “memos” are self serving and FAKE!” Trump tweeted.

Trump fired Comey last May, setting off a firestorm, as the Federal Bureau of Investigation was probing possible connections between Trump’s 2016 presidential campaign and Russia’s meddling in the American elections.

Russia has denied interfering in the election and Trump has denied any collusion or improper activity.

Reuters and other news outlets have obtained copies of Comey’s book before its formal release this week. In it, Comey wrote that Trump, in a private meeting, pressed the then-FBI director for his loyalty.

The FBI has long tried to operate as an independent law enforcement agency.