Germany has threatened to stop contributing development aid to countries that refuse to take back rejected asylum seekers.

The move comes in response to failings which kept the suspected Berlin Christmas market attacker from being deported to Tunisia.

"Those who do not cooperate sufficiently cannot hope to benefit from our development aid," Vice Chancellor Sigmar Gabriel told German weekly Der Spiegel in an interview published at the weekend.

German Interior Minister Thomas de Maiziere told ARD public television on Sunday that he "fully supports this idea".

The warning was aimed in particular at Tunisia - the home nation of Anis Amri, who was suspected of ploughing a lorry into a Berlin Christmas market last month in an attack that killed 12 people - and at north African nations in general.

Germany rejected Amri's asylum application last June, but Tunis initially denied he was a Tunisian citizen, blocking him from being sent home. A new Tunisian travel document for the 24-year-old only arrived two days after the slaughter in Berlin.

Several thousand citizens of north African nations, including those with almost no chance of obtaining asylum in Germany, are similarly lacking papers to return home.

The Christmas market attack has pushed the government of Chancellor Angela Merkel to consider how to improve the system.

Authorities are considering more routinely placing failed asylum seekers viewed as dangerous Islamists in detention ahead of their deportation.

"I will make very concrete proposals to expand the possibility of placing in detention people classified as dangerous before their expulsion," Justice Minister Heiko Maas said on Sunday, adding this would apply to failed asylum seekers whose countries were delaying taking them back.



Meanwhile, hundreds have protested in Tunisia this weekend against extremist Tunisian nationals who have travelled to fight in countries including Syria, Iraq, and Libya, from returning home.