FORT LAUDERDALE • The FBI was so caught up in the Russia probe that it failed to heed signs which could have prevented the Parkland school shooting, US President Donald Trump has said.
His comments come as he faces criticism from survivors of the attack over his ties to the powerful National Rifle Association (NRA), and after several thousand people rallied in Florida to demand urgent action on gun control.
"Very sad that the FBI missed all of the many signals sent out by the Florida school shooter. This is not acceptable," he wrote on Twitter late on Saturday.
"They are spending too much time trying to prove Russian collusion with the Trump campaign - there is no collusion. Get back to the basics and make us all proud!"
The US authorities have come under mounting scrutiny for failing to act on a series of warning signs ahead of the massacre at Marjory Stoneman Douglas High School in which 17 people were killed.
The Federal Bureau of Investigation admitted on Friday that it received a chilling warning last month from a tipster who said gunman Nikolas Cruz could be planning a mass shooting, but that agents failed to follow up on it.
It said a "person close to Nikolas Cruz" contacted the FBI's public access tipline on Jan 5 to "report concerns about him". The caller provided information about "Cruz's gun ownership, desire to kill people, erratic behaviour and disturbing social media posts, as well as the potential of him conducting a school shooting", the FBI statement said.
It added that the caller's information should have been "assessed as a potential threat to life" and should have been forwarded to its Miami field office, "where appropriate investigative steps would have been taken". "We have determined that these protocols were not followed for the information," the FBI said.
Attorney-General Jeff Sessions said he has initiated a Justice Department review of how the FBI acted. "It is now clear that the warning signs were there and tips to the FBI were missed," he said in a statement.
The attack has also renewed calls for greater gun control, with several survivors leading the charge.
One of them, 18-year-old Emma Gonzalez, delivered a fiery address to a crowd of students, parents and residents in Fort Lauderdale.
"To every politician taking donations from the NRA, shame on you!" she said, assailing Mr Trump over the multi-million-dollar support his campaign received from the gun lobby. The crowd chanted in turn: "Shame on you!"
"We are going to be the last mass shooting... We are going to change the law," she vowed, slamming the fact that 19-year-old Cruz was able to legally buy a semi-automatic firearm despite having a history of troubling and violent behaviour.
In Washington, the political response has made clear that the powerful NRA pro-gun lobby remains formidable, while Mr Trump suggested the root cause of mass shootings was a crisis of mental health - making no mention of gun control.
"If the President wants to come up to me and tell me to my face that it was a terrible tragedy and... how nothing is going to be done about it, I am going to happily ask him how much money he received from the National Rifle Association," Ms Gonzalez said in her speech.
"It doesn't matter because I already know - US$30 million (S$39 million)," she said, citing the sum spent by the NRA to support Mr Trump's election bid and defeat of Democrat Hillary Clinton.
There was no immediate response from the FBI to Mr Trump's latest allegation.
AGENCE FRANCE-PRESSE, BLOOMBERG