Trump will 'likely sue' over Mueller probe

US President Donald Trump says he likely will bring lawsuits against some of the people involved in the investigation into whether he or his 2016 election campaign colluded with Russia.

"I probably will be bringing a lot of litigation against a lot of people having to do with the corruption investigation having to do with the 2016 election," Trump told a joint news conference with Finnish President Sauli Niinisto on Wednesday.

Trump did not name names but has long expressed frustration at some of the central figures in the investigation by US special counsel Robert Mueller, such as former FBI director James Comey. Trump fired Comey in May 2017.

The Mueller probe found insufficient evidence to establish that Trump and his campaign had engaged in a criminal conspiracy with Russia.

The Russian state did run a hacking and propaganda operation to disrupt the US election, Mueller found.