President Donald Trump has launched a stinging attack on the FBI and US lawmakers over the investigation into Russian election interference, while seemingly politicising the Florida high school massacre.

In a series of tweets over the weekend, Mr Trump accused former president Barack Obama of failing to do enough to stop Russian election interference and belittled Adam Schiff, a member of the House intelligence committee investigating Russia’s actions.

Mr Trump labelled Mr Schiff – the ranking Democrat on the panel – a leaking “monster”.

The President argued that the ongoing investigations were what the Russians wanted, saying: “Investigations and Party hatred, they have succeeded beyond their wildest dreams. They are laughing their asses off in Moscow. Get smart America!”

He also claimed an excessive focus on Russia led FBI investigators to miss signs that could have prevented the deadly school shooting in Florida last week.

The tweets follow the announcement on Friday that special counsel Robert Mueller had charged 13 Russians and three Russian companies with a conspiracy to tamper in the 2016 US election.

The indictment says Russians adopted false online personas to push divisive messages and staged political rallies while posing as Americans, among other charges.

The document was silent on the question of whether anyone from the Trump campaign co-ordinated or worked with Russians to influence the election.

Russia has denied meddling in the US election, and Mr Trump has denied any collusion.

If it was the GOAL of Russia to create discord, disruption and chaos within the U.S. then, with all of the Committee Hearings, Investigations and Party hatred, they have succeeded beyond their wildest dreams. They are laughing their asses off in Moscow. Get smart America!

— Donald J. Trump (@realDonaldTrump) February 18, 2018

In a tweet on Saturday night, Mr Trump criticised the FBI for missing warning signs in the case of Nikolas Cruz, 19, who is charged with killing 17 people on Wednesday at Marjory Stoneman Douglas High School in Parkland, Florida.

More than a dozen people were wounded in the deadliest shooting at a US high school.

“Very sad that the FBI missed all of the many signals sent out by the Florida school shooter. This is not acceptable,” Mr  Trump said on Twitter.

“They are spending too much time trying to prove Russian collusion with the Trump campaign – there is no collusion,” he added.

Very sad that the FBI missed all of the many signals sent out by the Florida school shooter. This is not acceptable. 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!

— Donald J. Trump (@realDonaldTrump) February 18, 2018

Cruz was investigated as far back as 2016 after slashing his arm in a social media video, and saying he wanted to buy a gun, but authorities determined he was receiving sufficient support, US media outlets reported on Saturday.

The FBI acknowledged on Friday that it failed to investigate a warning that Cruz possessed a gun and the desire to kill.

Mr Trump has been a frequent critic of the FBI, accusing it of partisan bias.

On Sunday, he tweeted his dissatisfaction the agency still has not charged his Democratic rival Hillary Clinton with crimes related to her use of a private email server.

General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only Collusion was between Russia and Crooked H, the DNC and the Dems. Remember the Dirty Dossier, Uranium, Speeches, Emails and the Podesta Company!

— Donald J. Trump (@realDonaldTrump) February 18, 2018

– With AAP