Responding to growing pressure in Europe, Facebook is opening a new probe into Russian interference in Britain’s 2016 referendum on leaving the European Union.

A Facebook executive confirmed the existence of a formal investigation Wednesday in a letter to Damian Collins, a member of the British Parliament.

Collins had previously complained that the social network had been focused on U.S. election meddling and hadn’t dug deeply enough into Russian meddling in European affairs. In November, a Facebook executive said she had “seen nothing” to suggest Russian involvement in Brexit on Facebook. The following month, Facebook surfaced a tiny amount of evidence: The company said that the Internet Research Agency, a Russian “troll farm,” spent less than a dollar on three Brexit-related ads.

“You expressed a view that there may be other similar coordinated activity from Russia that we had not yet identified through our investigation and asked for us to continue our investigatory work,” Facebook's U.K. policy director, Simon Milner, wrote to Collins in a letter that was published by Business Insider. “We have considered your request and can confirm that our investigatory team is now looking to see if we can identify other similar clusters engaged in coordinated activity around the Brexit referendum that was not identified previously.”

Facebook found that the Internet Research Agency had engaged in an aggressive influence campaign ahead of the 2016 presidential election in the United States. The group spent roughly $100,000 on thousands of ads that reached over 10 million Facebook users. The operatives also pumped out a huge amount of free content that was seen by up to 126 million Facebook users, the company has said.

U.S. technology giants are facing increased pressure from lawmakers in the United States and Europe over the exploitation of their platforms, including the spread of fake news and the use of inauthentic accounts, during elections and other major public events.

The reopening of the Brexit inquiry could prompt additional inquiries in the United States. Facebook’s letter confirms that the company will begin to look for evidence of meddling beyond the Internet Research Agency. If the company finds evidence of other troll farms, it may prompt U.S. lawmakers to reopen their investigations.

In the coming days, Twitter plans to notify users who may have been exposed to Russian content, an executive said at a congressional hearing Wednesday. Facebook released a similar tool in late December.