His page - established in September - has 3.2 million likes.
Last week, the Phnom Penh Post reported that the majority of Hun Sen`s recent likes were from foreign accounts.
The biggest single groups of likes came from Indian accounts (255,692), with significant numbers also from the Philippines (98,256), Myanmar (46,368), Indonesia (46,368) and several others, the Post reported.
As well as their fierce political rivalry, Hun Sen and opposition leader Sam Rainsy, who lives in exile, are social media competitors too.
Both hope to win over the country`s huge young electorate, which in 2013 voted largely for Mr Rainsy`s Cambodia National Rescue Party (CNRP), who narrowly lost the election, which they claimed was rigged.
Mr Rainsy`s page has 2.3 million likes - significantly fewer than the prime minister, but most are from Cambodian accounts.
After the Phnom Penh Post report, the opposition leader accused Hun Sen of hiring foreigners to create fake accounts and increase the number of fans of his page.
Speaking at a university graduation on Thursday Hun Sen flatly denied this saying: "I don`t know where those `likes` are from."
Mr Rainsy was, he said, a "loser who doesn`t agree to lose".
"If I could buy India, I must be really strong. But I am just happy that I, Hun Sen, have been recognised by Indian people and people in other countries as the Prime Minister of Cambodia," he added.
Although Facebook bans the practice and carries out periodic purges of fake accounts, it is possible to buy likes from so-called "click farms", where people are paid small sums to create fake accounts whose likes and follows are then sold.
Celebrities, politicians and even a UK government minister have been accused of buying such social media approval.
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