Facebook said on Wednesday it would conduct a new, comprehensive search of its records for possible propaganda that Russian operatives may have spread during the run-up to Britain’s 2016 referendum on EU membership.

Some British lawmakers had complained that the world’s largest social media network had done only a limited search for evidence that Russians manipulated the network and interfered with the referendum debate.

Russia denies meddling in Britain’s vote to exit the European Union, known as Brexit, or in the 2016 U.S. elections.

Facebook, Twitter and Alphabet’s Google and YouTube have been under intense pressure in Europe and the United States to stop nations from using tech services to meddle in another country’s elections, and to investigate when evidence of such meddling arises.

Facebook’s new search in Britain will require the company’s security experts to go back and analyze historical data, Simon Milner, Facebook’s UK policy director, wrote in a letter on Wednesday to Damian Collins, chair of the British parliament’s Digital, Culture, Media and Sport Committee.

“We would like to carry out this work promptly and estimate it will take a number of weeks to complete,” Milner wrote.

Facebook said in December that it had found just 97 cents worth of advertising by Russia-based operatives ahead of Britain’s vote to leave the EU. Its analysis, though, involved only accounts linked to the Internet Research Agency, a suspected Russian propaganda service.

Collins last month described Facebook’s initial Brexit-related search as inadequate, and said on Wednesday he welcomed the company’s latest response.

“They are best placed to investigate activity on their platform,” he said in a statement. “I look forward to seeing the results of this investigation, and I’m sure we will want to question Facebook about this when we know the outcome.”

Facebook told U.S. lawmakers last year that it had found 3,000 ads bought by suspected Russian agents posing as Americans and seeking to spread divisive messages in the United States about race, immigration and other political topics.

In France last year, Facebook suspended 30,000 accounts in the days before the country’s presidential election to try to stop the spread of fake news, misinformation and spam.