US President Donald Trump slammed the FBI Saturday for failing to heed signs that could have prevented the Florida school shooting, charging the agency was too preoccupied with probing his campaign team over Russian election meddling.

Allegations of Russian interference in the 2016 presidential race and collusion with the Trump campaign are being investigated by several congressional committees and by special prosecutor Robert Mueller, who took charge of the federal government’s probe from the FBI last year following the sacking of its former chief James Comey.

“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.

“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!”

Troubled teen Nikolas Cruz killed 17 people with an assault rifle at his former high school in Parkland, Florida on Wednesday.

It was the 18th school shooting of the year and sparked renewed calls for gun control.

US authorities have come under mounting scrutiny for failing to act on a series of warning signs.

The FBI admitted Friday it received a chilling warning in January from a tipster who said Cruz could be planning a mass shooting, but that agents failed to follow up.

Cruz was also known to local police after his mother repeatedly reported him for violent outbursts, while records obtained by the South Florida Sun Sentinel show authorities investigated him in 2016 after he cut his arms on messaging app Snapchat and threatened to buy a gun.

Mueller’s investigation has so far swept up four members of Trump’s campaign, with two agreeing to work for the probe under a plea deal.

On Thursday Mueller indicted 13 Russians for allegedly running a secret campaign to tilt the vote, but did not accuse any Americans of knowingly participating in that effort.