SAN FRANCISCO (NYTIMES) - It's official: President Donald Trump is the single biggest political advertiser on Facebook.

Trump and his political action committee (PAC) spent US$274,000 (S$4374,246) on ads on the social network since early May, outpacing the second-biggest spender, Planned Parenthood Federation of America, a non-profit organisation that provides reproductive health care. Planned Parenthood spent just over US$188,000 on Facebook ads over the same period.

The ads bought by Trump and his PAC were also seen the most by Facebook's users, having been viewed by at least 37 million people since May. That compared with 24 million people who saw the second-most viewed group of political ads, which were also from Planned Parenthood.

These findings were laid out in a new study by researchers from New York University, who used Facebook's own data to arrive at the results. Facebook in May began an archive of political ads, which is a publicly searchable database that catalogues the ads and identifies which groups or individuals paid for them.

The NYU researchers broke out the top 449 spenders of political ads on Facebook since May for The New York Times. Of those, 210 were left-wing groups, 124 were right-wing groups and 115 groups were politically neutral, they said.

Damon McCoy, who conducted the study with two fellow researchers, Laura Edelson and Shikhar Sakhuja, said they were not able to tally the total spending for Republicans and Democrats because their analysis was ongoing, although they planned to release those figures in the future.

As the midterms approach, political consultants have said that Democrats who are running for election are spending a smaller percentage of their ad budgets on digital ads than their rivals, sometimes as little as 10 percent versus more than 40 percent for Republicans.

But the study found a healthy amount of activity from what the researchers described as left-leaning politicians.

Of the top 20 political candidates and PACs purchasing Facebook ads, 12 were identified as Democrats while eight were Republicans, according to data provided by the NYU researchers.