Campaigning by the two cities is reaching a peak ahead of an International Olympic Committee decision on September 13 on which of the two will host the 2024 Olympics.
French radio station RTL said Monday that the LA 2024 bid had used fringe internet companies to buy "likes", so it could announce that it had become the first Olympic bidder to attract more than one million Facebook fans.
Companies based in Pakistan, Bangladesh and Nepal are known to be used to buy social media "likes".
"All Facebook advertising has been purchased directly through Facebook. It's no surprise that this story originated from Paris," LA 2024 spokesman Jeff Millman told AFP in a statement.
"LA 2024 is a global campaign as the Olympic movement is global. There are Olympic stakeholders in every country.
"Bids advertise on traditional and social media, and all Facebook advertising has been purchased directly on Facebook."
The report documented a sudden boost in fans on the LA 2024 Facebook page, increasing from just over 200,000 at the end of 2016 to more than a million in April.
At the start of the year most of the LA "likes" had come from the United States but fans from developing countries such as Pakistan have dramatically increased.
Millman said there was a logical explanation to the sudden spike in "likes" from far off countries.
"Facebook advertising is more efficient in countries where there is less competition from other brands," he said.
"Since the IOC's international promotion period began on February 3, 2017, permitting bids to promote internationally, our promotion has been directed primarily internationally, including Facebook advertising around the world."
Reports of the spike in LA's social media popularity came as Los Angeles and Paris lobbied international sports leaders at the SportAccord convention in Denmark.
"We have done very little Facebook promotion in the United States since the international promotion period began on February 3, 2017. There are no eligible IOC voters in the United States," added Millman.
"All eligible IOC member voters live outside the United States, including Pakistan."
Over the same period, Paris also saw its fans grow threefold but 80 percent of its new Facebook "likes" came from France with many of the rest from francophone countries such as Algeria and Tunisia.
There is increasingly fierce competition between the US and French cities ahead of the September 13 vote.
On Tuesday, Paris paid for a front page advert on the international edition of the New York Times, drawing criticism from Los Angeles.
