Gab, the social media site popular with the far-right, has been forced offline by its service providers after it became clear that the alleged Pittsburgh shooter Robert Bowers had a history of anti-semitic postings on the site.

Formed in August 2016 after Twitter began cracking down on hate speech on its social network, Gab has been labelled “Twitter for racists” by the website Salon but describes itself as “a free speech website and nothing more”. But the platform has proved popular among white supremacists, neo-Nazis and the “alt-right”, including the man accused of opening fire on a synagogue in Pennsylvania on Saturday, killing 11.

“I can’t sit by and watch my people get slaughtered,” the alleged assailant wrote, moments before the murders. “Screw your optics, I’m going in.” It was his last post on the site.

In the hours following the attack, when the suspect’s postings were discovered on the site, Gab’s corporate partners abandoned it one by one. PayPal and Stripe, two of the company’s payment providers, dropped it, arguing that it breached policies around hate speech. PayPal said it takes “immediate and decisive action … when a site is explicitly allowing the perpetuation of hate, violence or discriminatory intolerance,” while Stripe said that the company had not provided sufficient evidence that it actually applies its moderation policies in practice.

Cloud-hosting company Joyent also withdrew service on Sunday, giving Gab 24 hours notice of its suspension, as did GoDaddy, the site’s domain registrar, which provides the Gab.com address. Both companies said the site had breached their terms of service.

GoDaddy added that it had “investigated and discovered numerous instances of content on the site that both promotes and encourages violence against people”.

Gab hit back, saying in a statement that the site is “under attack.”

“We have been systematically no-platformed by App Stores, multiple hosting providers, and several payment processors,” the company said in a statement posted to its site. “We have been smeared by the mainstream media for defending free expression and individual liberty for all people and for working with law enforcement to ensure that justice is served for the horrible atrocity committed in Pittsburgh.”

Gab is not the only social network accused of failing to apply its own policies against hate. On Saturday, Twitter apologised for its failure to take action against the chief suspect of a wave of attempted mail bombings, Cesar Altieri. He had been reported to the social network for threatening others, including journalist Rochelle Ritchie.

“Hug your loved ones real close every time you leave you home,” Altieri tweeted at Richie earlier this month, in one of many tweets reported for violating policies against threatening language. But Twitter took no action against Altieri’s tweets, a fact the company apologised for over the weekend.

“We made a mistake when Rochelle Ritchie first alerted us to the threat made against her,” the company said. “The tweet clearly violated our rules and should have been removed. We are deeply sorry for that error.”