US president Donald Trump lashed out at 16-year-old climate activist Greta Thunberg, a day after she was named by Time as its Person of the Year, calling her selection "ridiculous."
The Swedish teenager has become a symbol of a growing movement of young climate activists after leading weekly school strikes in her country that inspired similar actions in about 100 cities worldwide.
She has drawn large crowds with her fiery appearances at protests and conferences over the past year-and-a-half.
In a tweet this morning, Mr Trump said, "Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend!"
He added: "Chill Greta, Chill!"
Ms Thunberg responded by changing her Twitter profile bio to read: "A teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend."
She has been outspoken about her diagnosis with Asperger's syndrome, an autism spectrum disorder associated with high intelligence and impaired social skills.
"I have Aspergers and that means I'm sometimes a bit different from the norm," she tweeted this year. "And - given the right circumstances- being different is a superpower."
Former Secretary of State John Kerry, attending the United Nations climate talks in Madrid, said in an AP interview that Mr Trump's comments were "the most disgraceful, bullying, unpresidential, almost cowardly thing to do. And he should be ashamed of himself, but he knows no shame".
It is not the first time Mr Trump has complained after not being recognised for his influence. In 2015, Mr Trump attacked German Chancellor Angela Merkel for "ruining Germany" after she was named Person of the Year, when he was listed as a runner-up.
Mr Trump is the second world leader to take aim at Ms Thunberg this week. Her concern over the slayings of indigenous Brazilians in the Amazon drew a harsh rebuke from Brazil's president on Tuesday.
"Greta said that the Indians died because they were defending the Amazon," Jair Bolsonaro said. "It's impressive that the press is giving space to a brat like that," he added, using the Portuguese word "pirralha."
Ms Thunberg responded by changing her bio on Twitter, where she has over 3 million followers, to say "Pirralha".