WASHINGTON, July 22 (Xinhua) -- U.S. President Donald Trump on Monday renewed his attacks on Robert Mueller, days before the former special counsel is scheduled to testify before congressional panels about the Russia probe.

Trump said in a tweet that Mueller "should not be given another bite at the apple," claiming that "it will be bad for him and the phony Democrats in Congress who have done nothing but waste time on this ridiculous Witch Hunt."

The president also repeated a claim that Mueller's investigation found "NO COLLUSION, NO OBSTRUCTION!"

The former special counsel is set to testify publicly before the House Judiciary and Intelligence Committees on Wednesday and answer questions from lawmakers about his probe into alleged Russian interference in the 2016 U.S. presidential election and possible obstruction by Trump.

Mueller concluded his 22-month investigation in March by submitting a report to William Barr, who became Attorney General about a month earlier.

The report stated that there was no evidence that Trump's campaign conspired with the Russian government during the 2016 election but didn't conclude if the president had obstructed justice.

Instead, Mueller recounted 10 episodes involving Trump and discussed potential legal theories for connecting these actions to elements of an obstruction offense.

It was the Department of Justice that concluded that Mueller did not have "sufficient" evidence to support a charge in the obstruction case, a decision that has drawn scrutiny from Democrats, who have called for more investigations.