Germany is facing international embarrassment after it emerged that prison officials paid a convicted 9/11 accomplice €7,000 (£6,000) in cash.

Mounir al-Motassadeq is one of few people ever convicted over 9/11. He was deported from Germany last year after serving a 15-year sentence as an accessory to the 2001 attacks, in which almost 3,000 people were killed.

It has now emerged that before being flown to his native Morocco, the 44-year-old was handed €7,000 in cash as payment for prison work.

While prisoners are paid small amounts for work in Germany, Motassadeq should not have been eligible to receive the money because his assets are frozen as a convicted terrorist.

German prosecutors have opened an investigation against Till Steffen, the regional justice minister for Hamburg, on suspicion of violating the country’s anti-terror laws.

It appears the payment was an error as officials were used to treating Motassadeq as an ordinary prisoner and handed him the outstanding balance of his wages when he was released.