US investigators have met with a former British spy who compiled a salacious dossier on President Donald Trump’s alleged campaign ties to Russia, CNN reported on Thursday.

The investigators for independent special counsel Robert Mueller met with Christopher Steele this past summer, the news network reported, citing two people familiar with the matter.

Former FBI director Mueller leads a sweeping probe into possible Trump campaign collusion with Russian interference in the 2016 election.

"CNN has learned that the FBI and the US intelligence community last year took the Steele dossier more seriously than the agencies have publicly acknowledged," the network reported on its website.

The Wall Street Journal earlier identified former MI6 officer Steele as the author of the 35-page political research dossier which Trump branded as "fake news".