With a number of probes moving closer to the Oval Office, Donald Trump and his lawyer unleashed a fresh series of attacks on Sunday on the investigators, questioning their integrity while categorically ruling out the possibility of a presidential interview with the special counsel.

The US president and Rudy Giuliani used Twitter and television interviews to deliver a series of broadsides against special counsel Robert Mueller and federal prosecutors in New York.

Mr Giuliani said he was "disgusted" by the tactics used by Mr Mueller in his probe into Russian election interference, including in securing guilty pleas from the president's former national security adviser Michael Flynn on a charge of lying to federal investigators.

Mr Trump, Mr Giuliani said, would not submit to an interview by Mr Mueller's team.

"They're a joke," Mr Giuliani told "Fox News Sunday." "Over my dead body, but, you know, I could be dead."

The special counsel, who is investigating possible ties between the Trump campaign and Russia, has continued to request an interview with the president. Last month, the White House sent written answers in response to the special counsel's questions about possible collusion. The White House has resisted answering questions on possible obstruction of justice.