Russia will scrutinise the testimony of US Special Council Robert Mueller before Congress on Wednesday, said a senior diplomat, reiterating that Moscow had never meddled in the US vote.

"We will follow Robert Mueller's statements," Deputy Foreign Minister Sergei Ryabkov said, quoted by Russian news agencies.

"We will read them and see how what he says will differ from what is in the report."

Mueller headed the two-year probe investigating Russian meddling in the 2016 presidential election.

The report concluded that the Russian government interfered in the vote via hacking and social media.

Speculation swirls as to whether his testimony to lawmakers will incriminate US President Donald Trump and spell out clearly if he believes Trump obstructed justice.

FBI Director Christopher Wray on Tuesday warned that Russia intended to interfere in the elections next year as well, which Ryabkov denied.

"There are no grounds for the argument that Russia has tried to meddle or is planning to meddle... no, it is impossible," he said.