Facebook has removed campaign adverts by President Donald Trump and Vice President Mike Pence that featured an upside-down red triangle, a symbol used by Nazis to designate political prisoners in concentration camps.
Nathaniel Gleicher, the company's head of security policy, confirmed at a House Intelligence Committee hearing that the ads had been removed, saying Facebook does not permit symbols of hateful ideology "unless they're put up with context or condemnation".
"In a situation where we don't see either of those, we don't allow it on the platform and we remove it. That's what we saw in this case with this ad, and anywhere that that symbol is used, we would take the same action," Mr Gleicher said.
The advert began running on Wednesday.
In a statement, Trump campaign communications director Tim Murtaugh said the inverted red triangle was a symbol used by antifa so it was included in an ad about antifa. He said the symbol is not in the Anti-Defamation League's database of symbols of hate.
"But it is ironic that it took a Trump ad to force the media to implicitly concede that Antifa is a hate group," he added.
Antifa is an umbrella term for leftist militants bound more by belief than organisational structure.
Mr Trump has blamed antifa for the violence that erupted during some of the recent protests but federal law enforcement officials have offered little evidence of this.
Mr Gleicher appeared with representatives of Twitter and Google at a hearing centred on efforts by the technology companies to police the spread of disinformation, tied to both the election and Covid-19, on the platforms.
That is a significant challenge in a country facing potentially dramatic changes in how people vote, with expected widespread use of mail-in ballots creating openings to cast doubt on the results and even spread false information.
Facebook said on Thursday that it is working to help Americans vote by post, including by notifying users about how to request ballots and whether the date of their state's election has changed.
The Vote By Mail notification connects Facebook users to information about how to request a ballot. It is targeted at voters in states where no excuse is needed to vote by mail or where fears of the coronavirus are accepted as a universal excuse.
In working to facilitate postal voting during the pandemic, the company is stepping on to politically sensitive ground. Mr Trump and other Republicans are trying to limit such voting, while Democrats are pushing it to boost turnout.