Bulgarian authorities have detained five German citizens suspected of links to a terrorist organization after they entered the Balkan country from Romania, the state security agency said on Thursday.

Four have now been expelled and the fifth, a minor, is being looked after by social assistance authorities until he can be handed over to his family in Germany.

They had been travelling by train to Turkey when they were detained at the Kapitan Andreevo border checkpoint, the security agency said in a statement.

Four of the Germans were alleged to support a terrorist organization operating in Syria and Iraq. The minor was meant to reach Syria to join what the state security agency called a terrorist organization, it said without naming any group.

Bulgaria expelled 22 foreigners who were suspected of involvement in terrorist activities last year.

Thousands of West Europeans have travelled through Turkey in the past few years to join Daesh and other terrorist groups fighting in neighboring Syria.