Facebook says that a Russian troll farm with links to the Kremlin that spent $100,000 on Facebook ads in an attempt to influence U.S. politics only spent $0.97 targeting British voters ahead of the Brexit referendum. But the head of a parliamentary committee investigating fake news and online misinformation in the United Kingdom says he's concerned Facebook hasn't looked hard enough.

Responding to a request from the United Kingdom's Electoral Commission, Facebook said that three advertisements which were not explicitly related to the EU referendum, but to immigration, were targeted at Britons in the run-up to the referendum.

Facebook's investigation examined pages it identified as being run by the Internet Research Agency, a troll army based in St Petersburg that has ties to the Kremlin.

To target U.S. voters, the same group ran a wide network of Facebook, Twitter, YouTube, Instagram and Tumblr pages that were designed to look like real American activist groups. The troll group's content reached an estimated 150 million Americans on Facebook and Instagram alone, Facebook told the U.S. Congress.

Related: Seen any of these before? You may have been targeted by Russian ads on Facebook

For its investigation in the U.K., Facebook looked at ads placed during the official campaign period, which lasted just over two months, from 15 April to 23 June, 2016.

Damian Collins, who is head of the parliamentary committee that is investigating the role of fake news and online misinformation in the UK, said Wednesday that Facebook hadn't looked hard enough.

"It would appear that no work has been done by Facebook to look for other fake accounts and pages that could be linked to Russian backed agencies and which were active during the EU referendum," he tweeted shortly after Facebook's letter to the commission was released.

Collins said that by limiting its investigation to one Russian troll group and to the two month period leading up to the referendum, Facebook had not been thorough enough.

"Are we to believe that Russian backed targeting of voters through social media with fake news was limited only to Twitter during the EU referendum, when both Twitter and Facebook had been used by them in the USA during the Presidential election," he wrote.

In a speech last month, British Prime Minister Theresa May issued a warning to Russia saying that the U.K. believed it interferes in elections and plants fake news stories to sow discord. However, later in Parliament she clarified to say she was not talking about the U.K. specifically.

Facebook's findings were welcomed by pro-Brexit campaigners, including Nigel Farage, former leader of the United Kingdom Independence Party (UKIP).

"Where is the screaming conspiracy theory about Russia and the EU referendum, now we we know they spent less than £1 on Facebook?" he tweeted.

The Electoral Commission would not comment on Facebook's findings but said that it had received responses from Facebook, Twitter, and Google to their request for information relating to online misinformation in the U.K., and that "There is further work to be done with these companies in response to our request for details of campaign activity on their platforms funded from outside the UK."

While Twitter's response to the British electoral commission has not been made public, a CNN investigation in November found that a small number of Kremlin-linked accounts pushed pro-Brexit spin on the morning of the referendum.

Facebook has not provided the commission with the actual ads that were placed, but the social network told CNN it intends to. It did not respond to a request for comment regarding Collins' criticism.

Facebook's findings come at the end of a year when the company has had to come to grips with the spread of misinformation on its platform.

Just days after the U.S. presidential election in November 2016, Facebook CEO Mark Zuckerberg told a conference, "Personally, I think the idea that fake news on Facebook -- of which it's a small amount of content -- influenced the election in any way is a pretty crazy idea."

In January 2017, the U.S. intelligence community released a report which said that Russia tried to meddle in the presidential election and had used social media to do it. No similar assessment has been released in the U.K.

Facebook has since cooperated with multiple U.S. congressional investigations and has handed over the details of thousands of Russian-bought ads that targeted American voters and has pledged to take steps to increase transparency around political advertising on its platform.