The American anti-Islam campaigner David Horowitz donated $20,000 (€18,110) to the Dutch anti-immigration party PVV, run by Geert Wilders, in 2014, government documents show.
The donation from the David Horowitz Freedom Centre is the only one on the official home affairs ministry list of outside funding for the party last year.
Since 2013, Dutch political parties have been required by law to publish all donations over €4,500. The PVV was strongly opposed to the move at the time.
It is not the first donation Horowitz has made to Wilders. In 2012 he told Reuters news agency that he had paid Wilders for two speeches, but declined to say how much.
Horowitz is considered to be one of the most influential purveyors of anti-Islam propaganda in the US, alongside Pamela Geller who has also supported Wilders in the past. Geller, who believes US president Barack Obama is a secret Muslim, has invited Wilders to speak several times.
Daniel Pipes, who founded the pro-Israeli think-tank, The Middle East Forum, told Reuters in September 2012 he had funded police protection and paid legal costs for Wilders.
The PVV does not quality for official funding for political parties in the Netherlands because it has no membership structure. Wilders is the only official PVV member.