An FBI translator went rogue and travelled to Syria to marry an Islamic State (IS) group member whom she had been investigating, CNN has reported.

Daniela Greene soon returned to the US, where she served two years in jail.

Greene, now 38, had been working at the FBI’s Detroit office and investigating the IS recruiter since January 2014.

Six months later she travelled to Turkey, before crossing the border into Syria.

She had told her employers she was going to Germany to visit her parents.

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But soon after marrying Abu Talha al-Almani, the German IS member originally known as Denis Cuspert, or his rapper name Deso Dogg, Greene appeared to have second thoughts, emailing a contact: "I really made a mess of things this time."

By August, Greene had left Syria, and managed to get back into the US, where she was arrested.

"It's a stunning embarrassment for the FBI, no doubt about it," John Kirby, a former State Department official told CNN.

The details of the case were kept secret until now, when federal court records were released. Greene is now working in a hotel.

Greene's lawyer told CNN she is "smart, articulate and obviously naïve". He added that she was "genuinely remorseful" for what she had done.

Cuspert was originally pronounced dead by the Pentagon in October 2015, but six months later the military said he had survived the air strike in northern Syria.