The Kremlin views deteriorating Russian relations with the United States as one of the year's major disappointments, President Vladimir Putin's spokesman has said.

Ties between Moscow and Washington soured to reach a post-Cold War low following Russia's annexation of Crimea in 2014 and allegations of election meddling in 2016.

The two countries have been introducing tit-for-tat measures all year ranging from restrictions on embassy staff to legislation targeting state-owned media.

Asked about the Kremlin's biggest disappointments of 2017, Dmitry Peskov said worsening ties with the US are "certainly" on the list.

He reiterated the Kremlin's position that Russia seeks good relations with the US based on "mutual trust and mutual respect" but said "it takes two to tango".

In the US, special counsel Robert Mueller is leading the federal investigation into Russian interference in the 2016 election.

President Donald Trump has said he believes Mr Mueller "will be fair" to him.

He said "everybody knows that there was no collusion" between his presidential campaign and Russia.

Speaking to The New York Times, he said that Mr Mueller's probe - as well as two congressional investigations into the matter - have "angered" his base and "made the base stronger".

Mr Trump said some politicians "have been unbelievable in pointing out what a witch hunt the whole thing is".

The president repeated his assertion that Democrats "made the Russian story up as a hoax, as a ruse, as an excuse for losing an election that in theory Democrats should always win".