Online message board 8chan's fortunes worsened on Tuesday, as it was once again made homeless by a technical services provider and its owner was called to testify to the US Congress after 8chan was linked to a weekend mass shooting in El Paso, Texas.

The House of Representatives Homeland Security Committee demanded that owner Jim Watkins, an American living in the Philippines, testify about 8chan's efforts to tackle "the proliferation of extremist content, including white supremacist content."

The committee's Democratic chairman, Bennie Thompson, and Mike Rogers, its ranking Republican, sent a letter to Watkins to appear, calling the El Paso massacre "at least the third act of supremacist violence linked to your website this year."

8chan was offline on Tuesday after Seattle-based Epik became the latest provider to cut ties. In a statement, Epik's chief executive, Rob Monster, cited concerns about its inadequate enforcement and a greater possibility of violent radicalization.

In the heavily Hispanic city of El Paso on Saturday, a gunman killed 22 people at a Walmart store. Authorities have cited a lengthy anti-immigrant manifesto, apparently posted on 8chan by the suspect, as evidence of a racial motivate.

After the shooting, US cyber security firm CloudFlare withdrew services from 8chan, prompting it to sign up with Epik on Monday. Epik's own web infrastructure provider, Voxility, dropped it as a customer in response.

Epik still provides services to neo-Nazi site the Daily Stormer and "free-speech" site Gab, as well as InfoWars, a website run by conspiracy theorist Alex Jones.

Monster told Reuters the anonymity on 8chan differentiated it from other sites. "Nobody has a vested interest in personal accountability, since you always get a new persona," he said.

Fredrick Brennan, who created 8chan in 2013, has called for the site to be closed down. "If I could go back and not create 8chan at all, I probably would," he told Reuters in an interview, likening it to Frankenstein's monster.

In a reply to the House committee, a copy of which was posted on Twitter, 8chan's Watkins said he was always available to talk by telephone. "Rest assured I am not an extremist. My telephone should work worldwide," he said.

“This message was identified as spam.” Just making sure you received it, @HomelandDems. pic.twitter.com/8K3JNpHPzp

— 8chan (8ch.net) (@infinitechan) August 7, 2019

He argued earlier that the site provided a space for free speech.

"Think of 8chan as a large community of 1 million people that are now looking for a home," Watkins said in a video he posted on YouTube, with a shadowy likeness of American founding father Benjamin Franklin behind him.

Watkins said the Texas suspected gunman's manifesto was first uploaded not to 8chan but to Instagram, the photo-sharing app owned by Facebook.

A Facebook spokeswoman said the company has found "nothing that supports this theory" in an investigation since Saturday. Facebook disabled the suspect's Instagram account, which had not been active in more than a year, she added.