WASHINGTON — When an edited video of House Speaker Nancy Pelosi, D-Calif., began spreading across the internet this week, researchers quickly identified it as a distortion, with sound and playback speed that had been manipulated to make her speech appear stilted and slurred.

But in the hours after the social media giants were alerted, Facebook, Twitter and YouTube offered conflicting responses that potentially allowed the viral misinformation to continue its spread.

YouTube offered a definitive response Thursday, saying the company had removed the videos because they violated “clear policies that outline what content is not acceptable to post.”

Twitter declined to comment. But sharing the video would likely not conflict with the company’s policies, which permit “inaccurate statements about an elected official” as long as they don’t include efforts of election manipulation or voter suppression. Several tweets sharing the video, often alongside insults that Pelosi was “drunk as (a) skunk,” remained online Friday.

But Facebook, where the video appeared to gain much of its audience, declined Friday to remove the video, even after Facebook’s independent fact-checking groups, Lead Stories and PolitiFact, deemed the video “false.”

“We don’t have a policy that stipulates that the information you post on Facebook must be true,” Facebook said in a statement.

The company said it instead would “heavily reduce” the video’s appearances in people’s News Feeds, append a small informational box alongside the video linking to the two fact-check sites, and open a pop-up box linking to “additional reporting” whenever someone clicks to share the video.

That didn’t satisfy lawmakers such as Rep. David N. Cicilline, D-R.I., who took to Twitter to demand that Facebook “fix this now!”

While Facebook’s actions might provide context and lower the rate at which people will happen upon the video while browsing the social network, they did virtually nothing to prevent the false video’s spread by people who have already seen it: Any user could still like, comment, view and share the video as often as they liked.

In the 24 hours after The Washington Post alerted Facebook to the video, its viewership on a single Facebook page had nearly doubled, to more than 2.5 million views. The video had also been reposted onto other Facebook pages, where its audience was growing even further.