Many but not all of the posts mention billionaire investor and philanthropist George Soros, who was among the targets in a series of attempted bombings.
Researchers who study social media say they are seeing an increase in anti-Semitic posts from far-right users of Instagram and Twitter, and that the services aren't doing enough about it.
Separate researchers who were independently looking at the two social networks said that attacks on Jewish people had spiked on both services ahead of the Nov. 6 midterm elections, similar to a rise in harassment that occurred before the 2016 presidential election.
Many but not all of the posts mention billionaire investor and philanthropist George Soros, the researchers said. Soros is frequently the subject of unfounded conspiracy theories and his home was among the targets this week in a series of attempted bombings.
Jonathan Albright, a Columbia University researcher who directs a center on digital forensics, told NBC News that the amount of anti-Semitic material posted to Instagram and tied to Soros was possibly the worst sample of hate speech he had seen on the popular photo-sharing app.
The recommended top posts for the #soros hashtag on Instagram on Thursday included a photo of Soros with the caption, "I am the devil," and a cartoon suggesting that Soros and other targets of the explosive devices were themselves behind the bombs, a "false flag" conspiracy theory that gained traction online before the arrest of a Florida man on Friday.
Some captions for photos tagged #soros included explicit calls for violence against Jews, according to samples collected by Albright. "Life is about stabbing a Jew," read one caption from Oct. 10 that was still online on Thursday.
"What was shocking to me for this Soros tag were the nature of the images and the prevalence of hate speech in the captions," Albright said in a text message. "Especially this close to the 2018 election, and in spite of what happened last time around."
Albright, in a series of tweets, recommended that Instagram deactivate hashtags including #soros, remove imposter accounts and stop auto-filling its search bar with suggestions such as "soros jew."
Instagram, like its parent company Facebook, prohibits hate speech as well as content that "targets private individuals to degrade or shame them."
Instagram said on Friday that it was looking into Albright's findings and had taken down some material related to Soros that violated its policies, but the service said it hadn't seen a notable increase in impermissible material related to Soros.
"We are working closely with Facebook to understand the false content they are seeing, and applying those insights to Instagram to detect any policy-violating behavior. Any content which violates our Community Guidelines, for example hate speech, will be removed," Instagram said in a statement.
A separate study on Friday from the Anti-Defamation League, a nonprofit that fights discrimination against Jews, found a raft of anti-Semitic material on Twitter.
Samuel Woolley, a social media researcher who worked on the study, analyzed more than 7 million tweets from August and September and found an array of attacks, also often linked to Soros. About a third of the attacks on Jews came from automated accounts known as "bots," he said.
"It's really spiking during this election," Woolley, the director of the Digital Intelligence Laboratory, which studies "the intersection of technology and society," said in a phone interview. "We're seeing what we think is an attempt to silence conversations in the Jewish community."
The Anti-Defamation League also reported a "marked rise in the number of online attacks" against Jews based on interviews it conducted with five prominent Jewish Americans.
Twitter did not immediately respond to a request for comment on Friday.
Though the social network has purged millions of fake accounts during the past several months, Woolley, who previously studied social media as an academic at Oxford University, said the company needed to make a more concerted effort.
"Purging bots and getting rid of clear hate speech is not enough," Woolley said. "There needs to be more sophisticated methods of getting rid of defamation and organized propaganda efforts."
One of Soros' sons, Alexander Soros, wrote in the New York Times this week that the attempted bomb attack on his father was tied to the "demonization" of political opponents, which he said has gotten worse since Donald Trump's presidential campaign.