The founders of Facebook and Twitter have clashed following Twitter's decision to mark some of US President Donald Trump's tweets as "potentially misleading".
On Wednesday, , linking readers to a fact-checking page so they could "get the facts about mail-in ballots".
When asked about Twitter's fact-checking during an interview on Fox News, Facebook chief executive Mark Zuckerberg said his social network has a different policy.
"I just believe strongly that Facebook should not be the arbiter of truth of everything that people say online," Mr Zuckerberg said in a snippet of the interview posted online by Fox.
"I think, in general, private companies, especially these platform companies, shouldn't be in the position of doing that."
Twitter boss Jack Dorsey hit back at Mr Zuckerberg's comments on Thursday, saying Mr Trump broke Twitter's civic integrity policy, which does not allow "posting or sharing content that may suppress participation or mislead people about when, where, or how to participate in a civic process".
"Fact check: there is someone ultimately accountable for our actions as a company, and that’s me. Please leave our employees out of this," Mr Dorsey wrote.
"This does not make us an 'arbiter of truth'. Our intention is to connect the dots of conflicting statements and show the information in dispute so people can judge for themselves. More transparency from us is critical so folks can clearly see the why behind our actions."
Mr Dorsey went on to say Mr Trump's tweets "may mislead people into thinking they don't need to register to get a ballot", which is why Twitter marked them as such.
Mr Trump threatened to shut down social media companies following the incident, setting up a fresh challenge for the platforms as they struggle to deal with political misinformation during a toxic election campaign.
Social media's conundrum
The president's angry response and threat to "strongly regulate" or "close down" social media firms highlights the conundrum for Twitter and other platforms, said Steven Livingston, director of the Institute for Data, Democracy, and Politics at George Washington University.
Mr Livingston said he expects Twitter to narrowly enforce its misinformation policies, dealing only with specific issues such as the electoral process and the coronavirus pandemic.
The attacks by Mr Trump and his supporters put "so much pressure [on Twitter] and they are blanching at the thought of taking the next step" on curbing political misinformation, Mr Livingston said.
"They are caught on the horns of a dilemma and don't know which way to go."
Even while Twitter is pledging to foster a "healthy conversation" by filtering out hoaxes and toxic content, Livingston said the economic model for social platforms suggests the opposite.
"Platforms know very well they are accentuating extremism," he said. "Extremism holds attention and allows them to sell more advertising, and that's the whole point of the game."
University of Texas social media researcher and professor Samuel Woolley nonetheless welcomed what he called "a very bold move by Twitter" in the face of political pressure.
"Twitter will face a lot of backlash and whether they can bear up on this remains to be seen," he said.
Karen Kornbluh, head of the digital innovation and democracy initiative at the German Marshall Fund of the United States, said Twitter's action on content after it goes viral "may be a case of closing the barn door after the horse is out - but at least it communicates standards for acceptable activity on a platform's site and that no one is completely exempt."
