Known as Crossfire Hurricane, the 2016 investigation into the US president's alleged Russia ties was launched by the agency

US President Donald Trump has ordered the declassification of all FBI files related to the agency's investigation into his first election campaign's alleged contacts with Russia.

The FBI launched the 'Crossfire Hurricane' investigation in July 2016 to examine whether Trump - then a presidential candidate - or members of his campaign were colluding or coordinating with Moscow to influence the election.

In a memorandum released on Tuesday by the White House, Trump directed the Attorney General to make the materials available to the public "immediately."

Crossfire Hurricane was prompted by the 'Steele Dossier' - a compilation of unverified rumors about Trump and his alleged links to Russia. The dossier was compiled by former British intelligence officer Christopher Steele, and reportedly funded by the Hillary Clinton campaign.

Crossfire Hurricane preceded the appointment of Special Counsel Robert Mueller, whose subsequent 'Russiagate' investigation found no evidence of collusion between the Trump campaign and the Russian government.

In 2023, the US Justice Department's (DOJ) special counsel John Durham - appointed to review the origins of the Crossfire Hurricane probe - concluded that the FBI and DOJ had "failed to uphold their mission" by relying on biased information to surveil Trump.

Durham criticized the FBI for showing a "serious lack of analytical rigor," particularly when handling information from politically-affiliated sources.

It was also revealed that the Steele Dossier had been used by the FBI to obtain court permission to spy on Trump's campaign. In 2019, Justice Department Inspector General Michael Horowitz reported that the FBI had made "basic, fundamental, and serious errors" in its warrant application.

'Crossfire Hurricane' and Mueller's Russiagate investigation cast a long shadow over Trump's presidency, with allegations of "Russian collusion" persisting in the media even after Mueller's report found no evidence to back them up.

READ MORE: FBI should never have investigated Trump - report

In a video posted on Tuesday on Truth Social, Trump said after signing the order: "This was total weaponization. It's a disgrace...but now you'll be able to see for yourselves."

Addressing journalists, he added: "You probably won't bother because you're not going to like what you see."

Trump had previously ordered a full declassification of Crossfire Hurricane during the final days of his first term, but the documents were never released. According to a 2023 CNN report, a binder containing highly classified information later went missing.