US President Donald Trump declared on Sunday that Special Counsel Robert Mueller "should not testify" before Congress on his investigation into Russia's interference in the 2016 elections.

The House Judiciary Committee has asked Mueller to testify on May 15 about his 22-month-long investigation, which found that Trump attempted to thwart the probe but was silent on whether he should be charged with obstruction of justice.

"There was no crime, except on the other side (incredibly not covered in the Report), and NO OBSTRUCTION. Bob Mueller should not testify. No redos for the Dems!" Trump tweeted.