WASHINGTON - US President Donald Trump accused social media companies of interfering with the upcoming 2018 midterm election, without appearing to offer any evidence, telling the Daily Caller in an interview published on Wednesday that they are "super liberal."Referring to such companies, which include Facebook Inc and Twitter Inc, Trump told the conservative news outlet in an interview conducted on Tuesday that "I think they already have" interfered in the Nov. 6 election. The report gave no other details.The Republican president's accusation added to recent charges he has made of political bias against him by social media companies and search engines. Google and other tech companies have denied any political bias."The true interference in the last election was that — if you look at all, virtually all of those companies are super liberal companies in favor of Hillary Clinton," he added, referring to his Democratic opponent in the 2016 White House contest. US intelligence agencies have concluded that Russia interfered in the 2016 campaign with the aim of tilting the election in Trump's favor, a finding that Moscow has denied.