Berlin (CNN) -- A 48-year-old German man admitted being the father of his stepdaughter's eight children Tuesday, but denied he had sexually abused her, a German court official said.
The man, identified only as Detlef S., is on trial in Koblenz, Germany, charged with the sexual abuse of dependents and facilitating the sexual abuse of minors.
He is accused of hundreds of incidents of sexual abuse of his daughter, his stepdaughter and his stepson between autumn 1987 and summer 2010.
He is also charged with bringing his underage stepdaughter and his daughter to men who paid for sex with them on multiple occasions.
The first allegations of abuse came more than a decade ago, in 1998, but there was no medical evidence to support the claims then, Germany's youth welfare office said in a statement Tuesday after the trial opened.
Two stepsons leveled fresh accusations in 2002, saying the defendant was abusing his biological daughter, then 11. Police began an investigation but found no medical evidence and dropped the case, the statement said.
The daughter denied having been abused, the welfare office said.
It would not be against the law for the defendant to have a consensual sexual relationship with his stepdaughter, the office added.
Two men are due in court on charges of sexual assault in connection with the case. A third man suspected of abusing the children has died, Koblenz state court spokesman Alexander Walter said.
The trial of Detlef S. opened Tuesday, with his stepdaughter and stepson in court. His biological daughter was not present, Walter said.
The stepdaughter is giving evidence against him, the court spokesman said.
DNA test results introduced in court gave a "99.999%" certainty that the defendant is the father of her children, he said, and Detlef S. admitted Tuesday he was the father. But he denied the charges of sexual abuse, Walter said.
Seven of the stepdaughter's eight children survived infancy, he said. He did not know the cause of death of the eighth.
The sexual assaults took place in the defendant's home, in woods nearby and in various apartments near where the family lived, prosecutors charge.
Only two of the 350 charges are related to the stepson, Walter said.
The case is due to run through February 25, he said.
One of the men accused of paying for sex with the children is due to go on trial March 18, he added.
CNN's Roman Lehberger contributed to this report.