SOFIA, March 13 (Reuters) - Bulgarian nurses and a Palestinian doctor could have to spend three more years in a Libyan prison even if they overturn their death sentences for infecting children with HIV, their lawyer said on Tuesday. The six medics are being sued for defamation by three Libyans who claim the Bulgarians and Palestinian falsely accused them of torturing the six to confess. "If the court finds them guilty of defamation and sentences them to the highest punishment of three years in prison they will have to serve that time," Bulgarian national radio quoted defence lawyer Othman Bizanti as saying. "The court will not take into account the fact that they have already spent eight years behind bars," he said. Bulgarian officials have called the defamation case cynical. Prosecutors in Sofia have launched a case against 11 Libyans who they said tortured the nurses to confess they deliberately infected 426 children with the deadly virus. A Libyan court has postponed until March 25 a hearing on the defamation case. Bizanti said he expected Libya to open the medics' appeal against the death sentences at the end of April or early May. Bulgaria and its allies in Brussels and Washington say the medics are innocent and have stepped up diplomatic pressure on Libya to release them. Libya has indicated it may free the nurses if an agreement is reached to pay compensation to the families of the children.