The bosses of Amazon, Apple, Facebook and Google have fended off accusations that their companies stifle competition, under intense questioning from politicians who have been investigating Big Tech’s market dominance.

Amazon’s Jeff Bezos, in his first appearance before Congress, Facebook’s Mark Zuckerberg, Sundar Pichai of Google and Tim Cook of Apple sometimes struggled to answer questions about their business practices even as they provided data highlighting how competitive their markets are and the value of their innovation and essential services to consumers.

They also confronted a range of other concerns about alleged political bias, their effect on US democracy and their role in China.

The scrutiny of Big Tech could lead to new restrictions on its power, though forced breakups appear unlikely.

The four CEOs were testifying remotely at a hearing of the House Judiciary subcommittee on antitrust, while most politicians sat, in masks, inside the hearing room in Washington.

Among the toughest questions for Google and Amazon involved accusations that they used their dominant platforms to scoop up data about competitors in a way that gave them an unfair advantage.

Mr Bezos said that he could not guarantee that Amazon had not accessed seller data to make competing products, an allegation that the company and its executives have previously denied.

Regulators in the US and Europe have scrutinised Amazon’s relationship with the businesses that sell on its site and whether the online shopping giant has been using data from the sellers to create its own private-label products.

“We have a policy against using seller specific data to aid our private label business,” Mr Bezos said in a response to a question from Pramila Jayapal, a Washington Democrat. “But I can’t guarantee to you that that policy hasn’t been violated.”

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Google CEO Sundar Pichai testifies remotely (Mandel Ngan/Pool via AP)

Mr Pichai’s opening remarks touted Google’s value to “mom-and-pop businesses” in Bristol, Rhode Island and Pewaukee, Wisconsin, in the home districts of the antitrust panel’s Democratic chairman, Rhode Island Rep David Cicilline, and its ranking Republican, Rep James Sensenbrenner of Wisconsin.

But the Google executive struggled as Mr Cicilline accused the company of leveraging its dominant search engine to steal ideas and information from other websites and manipulating its results to drive people to its own digital services to boost its profits.

Mr Pichai repeatedly deflected Mr Cicilline’s attacks by asserting that Google tries to provide the most helpful and relevant information to the hundreds of millions of people who use its search engine each day in an effort to keep them from defecting to a rival service such as Microsoft’s Bing.

Facebook, in turn, faced renewed focus on its gobbling up of competitors. Jerrold Nadler, the Democrat who heads the House Judiciary Committee, told Mr Zuckerberg that documents obtained from the company “tell a very disturbing story” of Facebook’s acquisition of the Instagram messaging service.

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Facebook CEO Mark Zuckerberg speaks via video conference (Graeme Jennings/Pool via AP)

He said the documents show Mr Zuckerberg called Instagram a threat that could “meaningfully hurt” Facebook.

Mr Zuckerberg responded that Facebook viewed Instagram as both a competitor and a “complement” to Facebook’s services, but also acknowledged that it competed with Facebook on photo-sharing.

Some critics of Facebook have called for the company to divest Instagram and its WhatsApp messaging service.

As Democrats largely focused on market competition, several Republicans aired longstanding grievances that the tech companies are censoring conservative voices and questioned their business activities in China.

“Big Tech is out to get conservatives,” said Rep Jim Jordan of Ohio.

In a tweet before the hearing, President Donald Trump challenged Congress to crack down on the companies, which he has accused, without evidence, of bias against him and conservatives in general.

“If Congress doesn’t bring fairness to Big Tech, which they should have done years ago, I will do it myself with Executive Orders,” President Trump tweeted.