In a blog post by the firm's global politics and government outreach director, the company admitted it was "too slow to recognise" alleged Russian attempts to interfere in the US presidential election.
Answering the "hard" question of "What effect does social media have on democracy?", Facebook's Samidh Chakrabarti said: "While I'm an optimist at heart, I'm not blind to the damage that the internet can do to even a well-functioning democracy.
"It's abhorrent to us that a nation-state used our platform to wage a cyberwar intended to divide society."
Mr Chakrabarti noted that "Russian entities set up and promoted fake Pages on Facebook to influence public sentiment - essentially using social media as an information weapon."
Facebook told a congressional inquiry that 80,000 posts made by Russian-based entities were seen by up to 126 million of its users ahead of the presidential election.
In the UK, Facebook has been criticised for not investigating whether accounts other than those identified to have attempted to influence the presidential election had attempted to interfere in the Brexit referendum.
In response to a parliamentary inquiry into the fake news phenomenon, Facebook claimed that only three Kremlin-linked accounts were found to have bought advertisements which could have influenced the Brexit vote.
These accounts spent $0.97 (72p) on advertisements, it said.
The company is now widening its probe to identify further accounts which could have been involved in interference.
To deal with fake news, Facebook has suggested surveying users to establish which news sources are trustworthy, although this seems obviously as vulnerable to organised manipulation as the existing situation.
Facebook and Twitter have both published images showing similar influence attempts, but no evidence revealing Russian state culpability for the social media campaigns has yet been published.