Facebook Chief Executive Officer (CEO) Mark Zuckerberg on Wednesday fired back at United States President Donald Trump for accusing his firm of being "anti-Trump."

Trump, in an early morning post on popular micro-blogging site Twitter, brandished the leading social networking site as always being anti-Trump and called it "Fake News."

"Facebook was always anti-Trump.The Networks were always anti-Trump hence,Fake News, @nytimes(apologized) & @WaPo were anti-Trump. Collusion?" Trump wrote in his tweet.

Zuckerberg, in a Facebook post, rejected the idea that Facebook was biased, and said that the social networking site is working to ensure "free and fair elections" with an online platform that does not favour one side over another.

Mark Zuckerberg and other business leaders oppose Trumps order to end DACA
Facebook CEO Mark Zuckerberg

"Trump says Facebook is against him. Liberals say we helped Trump," Zuckerberg said in his post.

"Both sides are upset about ideas and content they don't like. That's what running a platform for all ideas looks like," he added.

Facebook was accused of letting fake news flow freely on its site during the run-up to the US Presidential elections last year, contributing to a Trump win.

Reports also emerged last week that Russia-funded advertisements on Facebook backed certain presidential candidates during the US presidential elections.

Donald Trump
U.S. President Donald TrumpREUTERS/Jonathan Ernst

The social networking site said that the information of the Russia-linked ads on Facebook would be handed over to the Congress for further probing. Reports state that the advertisements were targeted to build a drift among Americans over hot-button social issues during the time.

Facebook made its decision by stating clearly that it is cracking down on efforts to use its site to meddle with the elections in America or anywhere else.

A man poses with a magnifier in front of a Facebook logo on display December 16, 2015.REUTERS/Dado Ruvic/Illustration/File Photo

"After the election, I made a comment that I thought the idea misinformation on Facebook changed the outcome of the election was a crazy idea," Zuckerberg said.

"Calling that crazy was dismissive and I regret it. This is too important an issue to be dismissive," the Facebook chief said.

The United States Senate Intelligence Committee has asked the top tech companies Google, Facebook and Twitter to testify about Russian interference in US politics. The media giants are expected to appear on November 1 in an open hearing.