Michelle Obama has backed Swedish teen climate crisis activist Greta Thunberg and urged her to "ignore the doubters" after she was mocked by US President Donald Trump.
"Don't let anyone dim your light," the former first lady tweeted to 16-year-old Thunberg.
"Like the girls I've met in Vietnam and all over the world, you have so much to offer us all," she said.
Without mentioning president Trump, Michelle added, "Ignore the doubters and know that millions of people are cheering you on."
Thunberg, who has inspired protesters worldwide to push for action in combating the climate crisis, was named Time magazine's Person of the Year this week.
Trump on Thursday tweeted that it was "so ridiculous" for Thunberg to be recognised as Person of the Year.
"Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend! Chill Greta, Chill!" Trump wrote.
Following Trump's tweet, Thunberg updated her Twitter bio to reflect Trump's comments.
Democratic presidential frontrunner Joe Biden, who served as Barack Obama's vice president, chastised Trump for his comments, writing on Twitter, "What kind of president bullies a teenager?"
At the ongoing UN climate summit in Madrid, Thunberg accused rich countries of "misleading" the world over their response to climate change.