Donald Trump Jr. has liked a tweet which appears to blame the FBI for the school shooting in Parkland, Florida.

Nikolas Cruz, 19, killed 17 adults and children when he opened fire at Marjory Stoneman Douglas High School on Wednesday (14 February).

It is the nation's deadliest school shooting since the 2012 attack at Sandy Hook school in Connecticut and among the top 10 deadliest mass shootings in modern US history.

On Thursday (15 February), the president's son liked a tweet by conservative commentator Kurt Schlichter that suggested the FBI had been too preoccupied with undermining Donald Trump to prevent the school shooting.

"The FBI was too busy trying to undermine the president to bother with doing it's freaking job," Schlichter's tweet read.

The FBI was reportedly alerted about a person named Nikolas Cruz after he commented on a YouTube video that he was "going to be a professional school shooter". Officials have not confirmed whether the YouTube commenter is the same person as the alleged gunman, according to BuzzFeed News.

The FBI has spent recent months investigating claims that Russia interfered in the 2016 presidential election. Earlier this month, President Trump accused the bureau of being biased towards the Democrats.

"The top Leadership and Investigators of the FBI and the Justice Department have politicized the sacred investigative process in favor of Democrats and against Republicans, something which would have been unthinkable just a short time ago," he tweeted.

President Trump also suggested that the Parkland shooting could have been prevented, in a tweet earlier on Thursday: "So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behavior. Neighbors and classmates knew he was a big problem. Must always report such instances to authorities, again and again!"

At a press conference, he said that his administration was working to "tackle the difficult issue of mental health" and improve school security. The president made no reference to gun laws despite strong calls from families and politicians for tighter gun control.