"We think that is interesting but not determinative", said Alex Stamos, the company's chief security officer.
More than 290,000 accounts followed at least one of the pages and that about US$11,000 (S$15,000) had been spent on about 150 ads, Facebook said.
Facebook said it had contacted the admins involved and would alert the 2,600 users who had expressed interest in the event.
There was also coordinated activity around #AbolishICE, a leftwing campaign aimed at ending the Immigration and Customs Enforcement agency, the New York Times reported.
A man who identified himself as an administrator of Resisters, Washington activist Brendan Orsinger, said on a video call with Reuters that he had been invited to help operate the page by someone he knew only through Facebook messages.
COO Sheryl Sandberg said the company has deleted and removed 32 Facebook and Instagram accounts that engaged in coordinated efforts to mislead and manipulate people. "We disabled the event and reached out to the legitimate administrators of five other pages to let them know what's happened". The people responsible for these pages are doing a better job at covering their tracks, but Facebook says some of the activity is "consistent" with the behavior they saw the IRA doing during the run-up to the 2016 election.
A spokesman for Senate Judiciary Chairman Chuck Grassley said Facebook had informed his office that "that a limited group of Russian actors has attempted to spread disinformation using its platform and that the affected groups are affiliated with the political left".
Samples of the inauthentic activity.
▻ They ran about 150 ads for approximately $11,000 on Facebook and Instagram, paid for in USA and Canadian dollars.
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Nathaniel Gleicher, Facebook's head of cybersecurity policy, said that the activity bore some similarities to that of the Internet Research Agency, but that the actors had better disguised their efforts, using VPNs, internet phone services and third parties to purchase ads for them.
The company said that whoever set up the accounts "went to much greater lengths" to obscure their identities than the IRA had in the past, but also said it found links between some of the new accounts and previous Russia-linked accounts it had disabled a year ago.
These are important details, but on their own insufficient to support a firm determination, as we have also seen examples of authentic political groups interacting with IRA content in the past. He said the full extent of this effort may not yet be known. It has cracked down on fake accounts and tried to slow the spread of fake news and misinformation through outside fact-checkers.
Some accounts had connections to the Internet Research Agency (IRA) - the Russian-based group that interfered with the 2016 presidential election. Facebook pages with a few thousand followers, and Instagram accounts with no followers?
Facebook has been grappling with continuing public backlash for being slow to recognise Russian interference in the 2016 United States presidential election, along with widespread concerns over its past data-sharing practices.
In a series of briefings on Capitol Hill this week, the company told lawmakers that it detected the influence campaign on Facebook and Instagram as part of its investigations into election interference.
Facebook disclosed in September that Russians under fake names had used the social network to try to influence USA voters in the months before and after the 2016 election, writing about divisive issues, setting up events and buying ads.
- CNN's Nathan Hodge contributed reporting.