Lawmakers on Capitol Hill are pressing Facebook to abandon its plans to build a version of its Instagram app for kids and demanding the company share research into how Instagram affects teenage users.

Renewed scrutiny of Facebook's risks to teenagers' well-being was sparked by a Wall Street Journal story published Tuesday that revealed the social media giant's own research has found Instagram, the photo-sharing app it also owns, is particularly harmful to some teenage girls.

On Wednesday, Sen. Ed Markey of Massachusetts and Reps. Kathy Castor of Florida and Lori Trahan of Massachusetts, all Democrats, sent a letter to Facebook CEO Mark Zuckerberg raising concerns about the company's plans to launch a version of Instagram for users under 13. (Children are not allowed on the current app because of federal privacy law.)

They cited Zuckerberg's testimony at a March House hearing in which he claimed that research into the impacts of social media on children's mental health is not conclusive.

"Although you have publicly told Congress that 'the research [I have] seen is that using social apps to connect with other people can have positive mental-health benefits,' your own company's research points to disturbing relationships between Instagram use and young people's mental health challenges," Markey, Castor and Trahan wrote.

"Children and teens are uniquely vulnerable populations online, and these findings paint a clear and devastating picture of Instagram as an app that poses significant threats to young people's wellbeing," they wrote. "We are deeply concerned that your company continues to fail in its obligation to protect young users and has yet to commit to halt its plans to launch new platforms targeting children and teens."

They asked Zuckerberg to agree to abandon any plans for such platforms, including Instagram for younger users. They also asked whether he had "personally reviewed" Facebook's research on young users' mental health and requested he share copies of all internal and external research the company has conducted, commissioned or accessed.

Lawmakers, regulators and parents have criticized Facebook's plans for what it calls Instagram Youth since Buzzfeed first revealed the project in March. Child safety groups and 44 state attorneys general have called on Facebook to abandon the project, and lawmakers — including Markey, Castor and Trahan — have pressed the company over how it plans to protect the privacy and safety of users under 13.

Zuckerberg and other company executives have defended Instagram Youth, saying that because kids under 13 are already using Instagram regardless of the app's age limit, it would be better to make a version specifically for them and with parental controls.

The Journal's reporting, based on leaked internal Facebook documents, suggests the company is aware of the risks Instagram in particular presents to teenagers but has been reticent to make changes. The story cited a 2019 slide presentation summarizing the company's research that reads: "We make body image issues worse for one in three teen girls." Another said teens blame the photo-sharing app for higher rates of anxiety and depression.

The story has fueled anger among lawmakers over Facebook's lack of candor when the company was previously questioned about its effects on mental health.

"Mark Zuckerberg told me that he was aware of a 2019 study into rising suicide rates among young people during an Energy and Commerce Committee hearing – and this new piece illuminates the fact that our children, especially young girls, are still being harmed online, specifically on his very own platforms," Castor said in a statement.

On Tuesday, Sens. Richard Blumenthal, D-Conn., and Marsha Blackburn, R-Tenn., who also have pressed Facebook over child safety and mental health concerns, accused the company of having "provided evasive answers that were misleading and covered up clear evidence of significant harm."

They said they were in touch with a "Facebook whistleblower" and pledged to "investigate what Facebook knew and when they knew it."

Rep. Cathy McMorris Rodgers, R-Wash., who pressed Zuckerberg at the March House hearing about social media and mental health, also weighed in on Tuesday. She said she and fellow Republicans on the Energy and Commerce Committee requested Facebook's internal research back in March.

"Facebook refused to comply with our request and we now know why. This also leaves us wondering what else they are hiding," she said in a statement.

In a blog post on Tuesday, Karina Newton, Instagram's head of public policy, said The Journal's story "focuses on a limited set of findings and casts them in a negative light" but added that "we stand by the research."

She said both Facebook's internal research and external efforts to study the impact of social media on well-being is "mixed."

Editor's note: Facebook is among NPR's financial supporters.