German authorities say increasing numbers of North African jail inmates awaiting deportation are resorting to 'dirty protests' - smearing their cells with urine, blood and faeces.

Some guards at jails in Bielefeld, Aachen and Düsseldorf have also been attacked with human waste.

Some of the inmates - referred to by police as 'Nafris' for North Africans - were involved in the New Year's Eve attacks in Cologne when marauding mobs of immigrants sexually assaulted and robbed hundreds of women.

Guards at Aachen prison (pictured), near the Dutch border, have been targeted with human waste

North Rhine-Westphalia's justice minister Thomas Kutschaty submitted a report on the growing problem to the state parliament's committee on legal affairs this week.

There have been 32 cases of what is termed 'prison space pollution' from people originating in the Maghreb since the beginning of the year.

Those involved have been convicted of criminal offences and are serving their punishment before deportation.

Mr Kutschaty is urging a speeding up of the repatriation system as one way of defusing the situation inside the state's jails.