A student who survived the high school shooting that left 17 dead in Florida wants Donald Trump and Congress to “do something” about gun control, rather than simply offering thoughts and prayers to the victims of America’s latest mass shooting.

The president extended his “prayers and condolences to the families of the victims” on Twitter Wednesday afternoon, after a student opened fire on teachers and classmates at Marjory Stoneman Douglas High School in Parkland, Fla., approximately an hour earlier. The shooter, who was armed with an AR-15 semi-automatic rifle, killed 17 people in the massacre.

“No child, teacher or anyone else should ever feel unsafe in an American school,” Trump said in his tweet.

Student Sarah Chadwick, who was at the school during the attack, responded to Trump with a vehement demand for action.

“I don’t want your condolences you f---ing (piece) of s---, my friends and teachers were shot. Multiple of my fellow classmates are dead,” Chadwick wrote. “Do something instead of sending prayers. Prayers won’t fix this. But gun control will prevent it from happening again.”

In a televised address to the nation on Thursday, Trump reiterated his “deepest sympathies,” and said he’s making plans to visit Parkland and meet with families affected by the mass shooting.

Trump also said his administration will work with state and local officials to “tackle the difficult issue of mental health.”

“We are here for you….We are all joined together as one American family and your suffering is our burden also,” he said.

Many Twitter users joined Chadwick in condemning the flood of “thoughts and prayers” from right-leaning politicians following the shooting. “Thoughts and prayers have not helped any of the victims in the 29 school shootings this year,” wrote author Tony Posnacki. “Let me know when it is a good time to talk about gun control.”

Nevertheless, many politicians – the majority of them Republican – tweeted their thoughts and prayers after the shootings.

Trump himself often shares his “thoughts and prayers” or “prayers and condolences” with American victims, although he never mentions gun control or the National Rifle Association.

Last month, for instance, he issued a “thoughts and prayers” tweet following a mass shooting at a high school in Kentucky. The alleged shooter was a 15-year-old accused of killing two students and wounding 18 others.

“My thoughts and prayers are with Bailey Holt, Preston Cope, their families and all of the wounded victims who are in recovery,” Trump tweeted that same day, naming the two victims in his tweet. “We are with you!”

Trump also tweeted his “warmest condolences and sympathies” to the victims of the worst mass shooting in American history last October, in Las Vegas.

Trump suggested Thursday morning that the Florida shooting suspect, 19-year-old Nikolas Cruz, had mental health issues.

“So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior,” he tweeted. “Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!”

U.S. Attorney General Jeff Sessions called the shooting a “tragic event” on Thursday, adding: “We’re going to work on it in many ways to do something about it.”

Sessions spoke in generalities, and did not address reports that the weapon used in the shooting was acquired legally. Instead, he spoke of gang violence and the threat it poses to children.

“Parents have told me in a gang-infested neighbourhood that children can no longer stand on the bus stops by themselves,” Sessions said. “They take turns, the parents do, of being out there every morning and afternoon. So we’ve got to confront the problem.”

Parkland, Fla., was recently named No. 20 on Neighborhood Scout’s list of the 100 Safest Cities in America.

Florida Gov. Rick Scott said on Thursday he will talk with state lawmakers to make sure that individuals with mental illness “never touch a gun.”

“Our hearts and prayers are with these families,” he added.

The shooting suspect reportedly bragged about his guns on social media, according to students and neighbours. No one has suggested he is tied to a gang in any way.