In a decision published on Thursday, the Constitutional Court in Karlsruhe said it saw no problem with the deportation of non-German citizens thought to pose aterror risk.

The judges ruled that state interior ministries should be able to deport suspects without German citizenship speedily if they were considered to be a danger.

The decision hinged on a paragraph introduced into German residence legislation that allows accelerated deportations "to defend against a specific threat to the Federal Republic of Germany or a terror risk."

While the clause was added to the German Constitution after the September 11 terror attacks of 2001, it was only challenged in the wake of the Berlin Christmas market attack in December last year.

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The court was asked to consider whether the paragraph was constitutional in response to the case of an Algerian citizen who first arrived in Germany in 2003.

Earlier this year, the interior ministry of the German city of Bremen said it believed the man posed a risk and should be deported - a decision that was challenged at the constitutional level.

German-born, but still sent packing

The issue first came to light in the case of two men who were taken into custody in a raid in February in the German state of Saxony, in connection with what police said was a plot to carry out a "potentially imminent terror attack."

Both men were born in Germany but had foreign passports. The 27-year-old Algerian and 22-year-old Nigerian, who had been under surveillance for some time due to their alleged support for the "Islamic State" (IS) armed group, both lived with their parents in the northern German town of Göttingen.

The pair failed to win temporary legal protection from deportation in March, in a decision by the Federal Administrative Court in Leipzig.

rc/ng (dpa, Reuters)