U.S. cybersecurity company Cloudflare said on Monday it was terminating services to online message board 8chan after the suspected gunman in the weekend's El Paso shooting appeared to have used the website before he went on a rampage.

"We just sent notice that we are terminating 8chan as a customer effective at midnight tonight Pacific Time," Matthew Prince, CEO of Cloudflare, wrote in a blog post.

Cloudflare provides services to help web sites stay online and load faster. In particular, it provides protection against denial-of-service attacks, meaning when this protection is lifted, sites may be effectively taken offline. 8chan has been experiencing intermittent lengthy outages since Cloudflare pulled out.

On Saturday, a suspected shooter was said to have posted an anti-immigrant and anti-government screed on the forum before opening fire at a Walmart in El Paso, Texas, which left at least 20 people dead and another 26 wounded.

His post was deleted from one of 8chan's forums after the shooting started, but forum users archived the document, which contained a link to a PDF version, NBC News reported.

The suspect, identified as 21-year-old Patrick Wood Crusius, cited in his note that the gunman who killed 51 people at a mosque in Christchurch, New Zealand, in March was an inspiration, according to NBC News. The Christchurch shooter had live-streamed the attack online.

"Based on evidence we've seen, it appears that he posted a screed to the site immediately before beginning his terrifying attack on the El Paso Walmart killing 20 people," Prince wrote.

"8chan has repeatedly proven itself to be a cesspool of hate," he said.

Prince added that even if the online message board did not violate the law by refusing to moderate the "hate-filled" content uploaded by users, it created "an environment that revels in violating its spirit."

— Reuters and CNBC's Spencer Kimball contributed to this report.