US House Speaker Nancy Pelosi (D-Calif.) has stressed the need to continue investigations against President Donald Trump to find an “iron-clad” case to impeach him.

Pelosi emphasized on Wednesday that it was necessary that the investigation of Trump continued until they had found enough evidence to lodge a compelling case against him.

“What we do want to make is such a compelling case, such an iron-clad case, that even the Republican Senate, which at the time seems to be not an objective jury, will be convinced of the path that we have to take as a country,” Pelosi said on Wednesday.

US Special Counsel Robert Mueller said the two-year probe into Russia’s interference in the 2016 US presidential election had not cleared Trump of wrongdoings.

“If we had had confidence that the president clearly did not commit a crime, we would have said so,” Mueller added.

Trump, who is being methodically probed for evidence of his wrongdoings and cover-ups, admitted to Russia’s role in his election as US president in 2016.

US President Trump on Thursday acknowledged for the first time that Russia helped “me to get elected,” and then quickly retracted the idea.

Top Democratic lawmakers express opposing views over the timing of the impeachment.

Pelosi has been in favor of a slow approach towards the impeachment process,  while House Judiciary Committee Chairman, Jerrold Nadler (D-N.Y.), favors rapid legal action against Trump.