President Trump called 16-year-old climate activist Greta Thunberg a "very happy young girl" who has "a bright and wonderful future."

The president tweeted his sarcastic remark late Monday night, the same day the Swedish activist delivered an impassioned speech about climate change in front of the United Nations.

"She seems like a very happy young girl looking forward to a bright and wonderful future," the president tweeted, which quote-tweeted an excerpt of Thunberg's speech. "So nice to see!"

She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see! https://t.co/1tQG6QcVKO — Donald J. Trump (@realDonaldTrump) September 24, 2019

Trump and Thunberg went viral earlier in the day when the activist was caught glaring at the president as he arrived at the U.N. headquarters in New York City.

"You have stolen my dreams and my childhood with your empty words," she tearfully proclaimed to world leaders. "Entire ecosystems are collapsing, we are in the beginning of a mass extinction and all you can talk about is money and fairy tales of eternal economic growth. How dare you!”

Some pundits have accused environmentalists of manipulating a young girl for political purposes, including the Daily Wire's Michael Knowles, who stoked outrage by describing Thunberg as a "mentally ill Swedish child" who is being exploited by "the international Left."

Captured by @Reuters Andrew Hofstetter: @GretaThunberg watches Trump arrive at the #UNGA. Thunberg condemned world leaders for failing to take strong measures to combat climate change: ‘You have stolen my dreams’ https://t.co/e9VfOa2kwW pic.twitter.com/kbJqF4rvxc — Reuters Top News (@Reuters) September 23, 2019

Thunberg appeared in front of members of Congress in the House Ways and Means Committee last week. She is known for founding an international movement called Fridays for Future, which advocates for students to skip school on Fridays to protest climate change. New York City public schools announced ahead of time that they would rule absences from last Friday's climate change rally excused if parents consented.

During her travel to the United States, Thunberg opted to take an emissions-free solar-powered boat instead of flying to New York ahead of her speech next week.

The president has been at odds with many foreign leaders about climate change since he withdrew the U.S. from the Paris climate agreement in 2017.