"My name and the #FridaysForFuture movement are constantly being used for commercial purposes without any consent whatsoever," the 17-year-old Swede wrote on her Instagram account. 

"I assure you, I and the other school strikers have absolutely no interests in trademarks. But unfortunately it needs to be done."

She complained that "there are still people who are trying to impersonate me or falsely claim that they 'represent' me in order to communicate with high profile people, politicians, media, artists etc."

There had also been instances of marketing, product selling and people collecting money "in my and the movement's name," she wrote.

"That is why I've applied to register my name, Fridays For Future,... as trademarks. This action is to protect the movement and its activities."

Thunberg, whose protests have attracted millions of young people across the globe, also said she was setting up a non-profit making foundation to handle the financial side of "Fridays for Future", such as book royalties, donations and prize money. 

She insisted that the foundation would be "completely transparent," for example, with regard to the taxes it has to pay. 

"The foundation's aim will be to promote ecological, climatic and social sustainability, as well as mental health," the campaigner wrote. 

Thunberg's climate struggle began quietly in August 2018 when she skipped school for the first three weeks, and then on Fridays to spend the day outside Sweden's parliament with a sign labelled "School strike for climate".

Since then, she has become the face behind the global protest movement, particularly for young people. 

Thunberg has also come under ferocious attack from climate changes deniers, who accuse her of being manipulated by a "green lobby". 

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© Agence France-Presse