US President Donald Trump has said he supports the Federal Bureau of Investigation (FBI) "100 per cent", less than an hour after criticising the agency.During a speech at the FBI National Academy's graduation in Virginia, Trump heaped praise on the agency, saying it was full of "great people", BBC reported on Friday.His visit comes only days after he described the agency as "in tatters" and "the worst in history".Before travelling to the FBI campus on Friday, Trump said people were "very angry" with the agency's actions."The president of the United States has your back 100 per cent," he said later at the graduation ceremony in Quantico, Virginia."By the way, you are great people," he added. "I'd say like 90 per cent are great, right? The other 10 per cent, that's not working out so well."Earlier this month, Trump lambasted the agency and its former director, James Comey, whom he fired in May.On his way to Quantico on Friday morning, Trump struck a different tone, telling reporters that "its a shame what's happened with the FBI".He appeared to refer to recent reports that two FBI agents had privately exchanged text messages during the 2016 election, which included disparaging remarks about then-candidate Trump.Republicans have claimed that the text exchange proves an anti-Trump bias in the special investigation being led by former FBI director Robert Mueller, who is examining possible campaign collusion with Russia and meddling in the US election process. Trump denies that his team colluded with Russia to get him elected.The two agents also reportedly insulted Democrats Bernie Sanders and Hillary Clinton, as well as other prominent political figures, according to the contents of the text messages released to US Congress and obtained by US media.FBI regulations state that agents are permitted to express opinions "as an individual privately and publicly on political subjects and candidates".