Most of the posts focused on sowing political and social divisions, the firms have said.
The companies said they used a combination of staff and big data to police that content, disabling fake and spam accounts.
“These actions run counter to Facebook’s mission of building community and everything we stand for,” Mr Stretch said on Tuesday.
In a blog post from earlier this month, Facebook’s Elliot Schrage said that many of the posts did not violate the company’s content policies. They were removed, he said, because they were inauthentic – the Russians behind the posts did not identify themselves as such.
Senator Al Franken, Democrat from Minnesota, asked Facebook – which absorbed much of lawmaker heat – why payment in Russian rubles did not tip off the firm to suspicious activity.
“In hindsight, we should have had a broader lens,” Mr Stretch said. “There are signals we missed,”
Key recent developments:
Nov 2016: Facebook founder Mark Zuckerberg says “the idea that fake news on Facebook influenced the (US) election in any way is a pretty crazy idea”
Aug 2017: Facebook says it will fight fake news by sending more suspected hoax stories to fact-checkers and publishing their findings online
Oct 2017: Google finds evidence that Russian agents spent tens of thousands of dollars on ads in a bid to sway the election, reports say
Oct 2017: Twitter bans Russia’s RT and Sputnik media outlets from buying advertising amid fears they attempted to interfere in the election