(CNN) -- Libya must make arrangements to hand over Saif al-Islam Gadhafi to the International Criminal Court immediately, court officials said Thursday, complaining that the son of Libya's deposed leader has been mistreated and "physically attacked" since he was captured last year.
Gadhafi is in a "legal black hole," held for 139 days in "total isolation" except for visits from officials, his ICC-appointed defense said in a strongly worded statement.
He also suffers dental pain because he hasn't had treatment, and Libyan authorities have given him nothing to remedy the pain, lawyers Xavier-Jean Keita and Melinda Taylor said.
"At no point have the Libyan authorities been legally justified in their failure to surrender him to the ICC," the lawyers said.
"The brutal death of Moammar Gadhafi deprived the Libyan people of their right to justice, and their right to the truth. It would be a travesty for the prospects of a free and fair Libyan state if the same were to occur to his son," they said.
Saif al-Islam Gadhafi was facing an arrest warrant from the ICC for alleged crimes against humanity at the time of his capture, and the court, based at The Hague in the Netherlands, is still seeking to prosecute him.
Domestic authorities told Gadhafi only that he was being investigated in Libya for "trivial allegations" of not having a license for camels and irregularities concerning fish farms, his ICC lawyers said. When the ICC requested that Libya surrender him to the court, Libyan authorities then said they wanted to prosecute Gadhafi for more serious crimes, Keita said.
ICC prosecutor Luis Moreno-Ocampo said it's possible that the court will allow Libya to proceed with its case if the Libyans explain their plans.
"According to the rules, Libya has the primacy to prosecute Saif, so if they present this to the International Criminal Court judges, probably they will get an approval," Moreno-Ocampo said on Thursday. "That's the system. The system is the primacy for the national judges."
Amnesty International called on Libya to hand over Gadhafi at once in light of the ICC statement.
"An unfair trial before a Libyan court where the accused could face the death penalty is no way to guarantee justice and accountability," the rights group said.
Amnesty said Libya did not have a functioning court system and the country was "unable to conduct effective investigations," so "the ICC will be crucial in delivering accountability in Libya."
Saif al-Islam Gadhafi, once his father's heir apparent, was captured in November and has been held in the Libyan city of Zintan since then.
Libya and the ICC have been going back and forth since his capture about where he will be tried.
Human Rights Watch said after visiting Gadhafi in custody last year that he should have a lawyer, but Interior Minister Fawzy Abdilal implied in February that he had not asked for one.
"He may have a lawyer if he asks for a lawyer," the interior minister told CNN in an exclusive interview. "Should Saif demand a lawyer, then a lawyer would be provided."