The exiled Cambodian politician Sam Rainsy has filed a legal suit against Facebook, demanding it hand over any information which could prove that the Cambodian prime minister, Hun Sen, purchased millions of “likes” to appear popular on the social media platform.

The lawsuit is the first time that Facebook has been sued for information regarding a world leader’s page, and could have major implications in Cambodia where Facebook is the main news source for many and hugely influential in politics.

Rainsy, who led the recently banned opposition Cambodia National Rescue party (CNRP) in the 2013 election and now lives in exile in France, was taken to court for defamation after he made the claim that Hun had misused the social media website to falsify his own popularity.

After joining Facebook in 2016 Hun’s page was one of the fastest growing on the site, with 3m likes within a matter of months. He now has over 9m likes and in a recent report his Facebook page ranked third in global engagement among world leaders.

However, analysis noted that 80% of the accounts that liked the prime minister’s page came from countries outside Cambodia, including, India, Mexico and the Philippines. These are places where click farms – companies that sell fake social media popularity – are known to operate.

Hun denied that this proved any of the likes were fake, stating that it was simply an indicator of his global popularity.

“We are counting on Facebook to help shed light on the regime’s manipulation of technology,” said Rainsy. “If Hun Sen has nothing to hide, he should support our investigation of his activities.”

Rainsy can legally apply to Facebook for the information – which the company, known for its strict privacy, would usually not give out – because it could be used as defence in his defamation case in Cambodia.

Rainsy’s lawyer Richard Rogers contacted Facebook 18 months ago to inform the company that there was a “real concern” that Hun Sen was manipulating the democratic process through Facebook by buying likes and giving a false impression of his popularity. He got no response from Facebook, so working with a San Francisco law firm he put the wheels in motion for the lawsuit.

Sam Rainsy, the former opposition leader, claims that Hun Sen misused Facebook to falsify his own popularity. Photograph: AFP/Getty Images

Rogers said the objective was to “uncover how the Hun Sen regime is misusing the platform to prop up its popularity and to give a false impression of its legitimacy. It’s important to set the record straight and the people of Cambodia have the right to know if their leader is manipulating them.”

The lawsuit also requests Facebook send any evidence of Hun disseminating propaganda though the platform, and using it to make threatening, abusive and harassing statements to Rainsy and his supporters, which directly violates Facebook’s code of conduct.

Rogers said that as Facebook became more and more powerful and relevant to political debates and issues “they can’t just stand by and say ‘this is nothing to do with us’. This is the promotion of fake news and propaganda by the authoritarian Hun Sen regime, using Facebook. They are helping to prop up a dictator.”

The lawsuit comes in the wake of the complete collapse of democracy in Cambodia. In December Cambodia’s top court ordered the CNRP, the only opposition party, to be dissolved, ensuring that Hun – who has been prime minister for 33 years – would have no opponents in the upcoming general election.

Hun also uses Facebook to disseminate his message to young people and target his critics. At least 15 people have been arrested in Cambodia over Facebook posts since 2014, and others have been threatened.

Should it be proved that Hun broke Facebook’s code of conduct, it could lead to his Facebook page being taken down. So far the only world leader whom this has happened to is Chechnya’s Kremlin-backed leader, Ramzan Kadyrov, whose Facebook account was taken down last month.

Facebook spokeswoman Genevieve Grdina declined to comment on the lawsuit, but noted that any page can target ads to an international audience. The company also blocks the registration of millions of fake accounts on a daily basis, she said, and has improved its systems to identify fraudulent users.

Sam Levin contributed reporting from San Francisco.