Twitter has told a parliamentary inquiry that it has found little evidence of Russian involvement in the 2016 EU referendum campaign.
Writing to Damian Collins MP, who is leading the Digital, Culture, Media and Sport (DCMS) Committee's inquiry into fake news and misinformation, the social media platform said it had examined accounts identified by City University as potentially being Russian state-sponsored.
But it said: "We do not have sufficiently strong evidence to enable us to conclusively link them with Russia or indeed the Internet Research Agency."
The Internet Research Agency is a Russian online influence agency.
Twitter also said: "If Twitter identifies further relevant information relating to the 2016 EU Referendum we will write to you and update your committee accordingly."
In reply, Mr Collins said that there were still some outstanding questions and wrote: "The failure to obtain straight answers to these questions, whatever they might be, is simply increasing concerns about these issues, rather than reassuring people."
The committee also announced details of an evidence session with the US tech giants that it will hold next month in Washington.
It will be the first hearing of a House of Commons select committee to be held outside the UK and will be broadcast live.
Representatives from Google, Facebook and Twitter will give evidence, along with executives from CNN, the New York Times and CBS News.
More from Brexit
Earlier this month, Facebook told the DCMS committee that it would expand its investigation into Russian activity on its platform during the Brexit referendum.
It had previously told the committee that only 70p had been spent by Russian accounts on adverts during the campaign but the committee demanded Facebook look again.