Facebook and Twitter have agreed to share information with the UK government about possible Russian interference in the 2016 Brexit referendum.
Facebook said it hoped to be able to respond to questions from the Electoral Commission by mid-December.
The Commission is investigating activity in the period leading up to the Brexit vote.
Twitter said it hoped to share its own findings "in the coming weeks".
The BBC understands that Google is also cooperating with the Electoral Commission's request.
The US is conducting a similar investigation into potential Russian meddling in the presidential election.
The two social media giants were responding to a letter from Damian Collins, chairman of the Digital, Culture, Media and Sport Select Committee, also requesting information about Russian-linked account activity in the build-up to the EU referendum.
Facebook's policy director Simon Milner said the firm was "considering how we can best respond" to the committee's request.
Mr Milner said Facebook was also "committed to assisting" a broader inquiry into fake news.
In his response, Twitter's UK head of public policy Nick Pickles added that Twitter was catching more than 3.2 million "suspicious accounts" per week and 450,000 suspicious log-ins per day.
However, he said it was important to note that "not all automated accounts are bad", citing as examples bots that tweet air pollution levels and Wikipedia edits.