On Sunday, the Parliament's Digital, Culture, Media and Sport (DCMS) Committee issued a report in which the panel members said they had heard some evidence pointing to a campaign to influence UK election and referenda, allegedly led by Moscow.
Mueller has been looking into the alleged Russian interference in the 2016 US presidential election and the purported collusion between the Russian government and the campaign of US President Donald Trump. The US president has repeatedly described the probe as a witch hunt.
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Russian officials have stressed that Moscow does not interfere in the internal affairs of other countries and pointed out that the allegations against Russia had not been substantiated.