WASHINGTON (Reuters) - U.S. President Donald Trump accused social media companies of interfering with the upcoming congressional elections, without appearing to offer any evidence, in an interview published on Wednesday ahead of congressional testimonies from top social media executives.

U.S. President Donald Trump arrives to speak at a campaign fundraising luncheon for Rep. Ted Budd (R-NC) and GOP congressional candidate Mark Harris at Carmel Country Club in Charlotte, NC, U.S., August 31, 2018. REUTERS/Yuri Gripas

Referring to companies such as Facebook Inc FB.O and Twitter IncTWTR.N, Trump, a Republican, told the Daily Caller in an interview conducted on Tuesday "I think they already have" interfered in the Nov. 6 election.

The report gave no other details.

Trump’s accusation added to recent charges he and Republican lawmakers have made of political bias against conservatives by social media companies and search engines.

“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 said, referring to his Democratic opponent in the 2016 presidential election.

Google and other tech companies have denied political bias.

Republican lawmakers may raise issues of political bias in Wednesday’s hearing in the Senate Intelligence Committee, where Facebook Chief Operating Officer Sheryl Sandberg and Twitter Chief Executive Jack Dorsey will testify.

The executives are expected to defend their companies against what lawmakers see as a failure to combat foreign efforts to influence U.S. politics.

U.S. 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.

The United States also has said foreign entities continue to attempt to sow discord in the U.S. political system.