DNA tests have confirmed that Josef Fritzl, the Austrian man who locked up his daughter in a cellar beneath his house for 24 years, was indeed the father of her six surviving children, investigators said today.

The tests were ordered at the weekend after the shocking case of kidnap and incestuous abuse came to light, although their result does not come as a surprise. Mr Fritzl, 73, had already confessed to having imprisoned his daughter, Elisabeth, and fathering a total of seven children by her, including a boy who died shortly after birth.

“The (DNA test) result... shows that the six children, which the unfortunate Elisabeth Fritzl gave birth to in the basement, have all been undoubtedly fathered by her own father, the now 73-year-old Josef Fritzl,” Colonel Franz Polzer, head of the criminal investigation unit in Lower Austria, told a news conference this afternoon.

Colonel Polzer said that police had today inspected other properties owned by the retired electrical engineer to make sure that he was not holding other captives in similar underground cells. None was found.

Earlier today Mr Fritzl was remanded in custody for 14 days after appearing today before a judge in St Poelten, the provincial capital of Lower Austria. He is not expected to be charged until the end of that period, but prosecutors said earlier that the charges could include "murder through lack of action" over the death of the baby boy.

Meanwhile, officials in Amstetten, the small town where the Fritzl family lived, that Mr Fritzl's victims - Elisabeth, her children and her own grown-up siblings - would be offered new lives and new names. "The name Fritzl has been muddied," said Hans-Heinz Lenze, head of the social services in the town.

Elisabeth Fritzl has told police that her father lured her into the cellar of their home in 1984, drugged and handcuffed her, and kept her imprisoned for almost a quarter of a century.

Three of those children, a girl aged 19, and two boys aged 18 and 5, have been locked in the cramped cellar with her since birth and had never seen sunlight until their release at the weekend. The three others - two girls and a boy - were brought out of the cellar and adopted to be brought up by Fritzl and his wife, Rosemarie.

The abuse came to light at the weekend when Fritzl apparently allowed the 19-year-old girl, Kerstin, out of the basement dungeon for treatment after she fell seriously ill. Doctors trying to explain her illness then issued an urgent appeal for her mother to come forward.

Doctors said today that Kerstin, who has been suffering from severe cramp brought on by lack of oxygen, was still in a critical state and no firm prognosis could be made for her.

The young woman is being treated at a different hospital to her mother and five siblings who were taken on Sunday, along with Rosemarie Fritzl, to the neurospsychiatric clinic at the Mostviertel Amstetten-Mauer regional hospital.

Doctors and officials said that the group were being kept in a "protected zone" at the hospital for their gradual reintroduction to the outside world. Paulus Hochgatterer, a child psychologist, said that they were "in a treatment container that can be locked from the inside".

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