BERLIN, August 14, 2008 (AFP) - A German court on Thursday sent a woman who killed her five sons to a secure psychiatric unit for an indefinite period, ruling she was mentally ill and therefore of diminished responsibility.

Steffi Kitzmuller, 32, killed her five children aged three to nine in December by giving them sleeping tablets and then suffocating them with rubbish bags.

The woman from near Kiel in northern Germany has been hearing voices since 2006 and killed her children in order to escape a 'demon in human form' called 'Natalie,' according to a psychiatrist's report presented to the court.

The case is the latest in a string of infanticides to have shocked the country.

The most notorious was Sabine Hilschenz, from eastern Germany, who is currently serving 15 years in prison for the manslaughter of eight babies. She kept their remains in buckets, flower pots and an old fish tank.