NEW YORK (AFP) - The US presidential race, dominated by firebrand Republican contender Donald Trump and former first lady Hillary Clinton, was the most discussed topic on Facebook this year, the site announced on Wednesday.

The Democratic and Republican parties may not have nominated their candidates yet and America is still a year from electing the next leader of the free world, but it's got the world's 1.5 billion Facebook users abuzz.

Billionaire former reality TV star Trump leads the Republican polls but has sparked international condemnation for insulting Mexicans, tussling with critics and demanding a ban on Muslims entering the United States.

Clinton, the former first lady, senator and secretary of state who heads polls for the Democrats, is also one of the most visible US politicians on the international stage.

Facebook said the list was based on how frequently a topic was mentioned in posts on the social networking site by its 1.5 billion active users across the world between January and December 2015.

The second most discussed topic was the November attacks in Paris, which killed 130 people, and third the war in Syria and the refugee crisis.

The Nepal earthquake, which killed nearly 8,900 people in the impoverished Himalayan nation in April, came fourth.

President Barack Obama was the most talked about politician, Trump second - an astonishing feat for a man who has never held public office - and Clinton fourth behind Brazilian president Dilma Rousseff.

Narendra Modi, prime minister of India - the world's largest democracy - came ninth just ahead of Israeli Prime Minister Benjamin Netanyahu.