Muammar Gaddafi's ailing son in good health
"I assure the world that Saif (al-Islam) is being given a humanitarian treatment with respect and according to human rights guidelines," said Abdurrahim El-Keib.
He further said that the government would give him a fair trial.
An arrest warrant against Saif-al-Islam was issued in 2011 for his alleged involvement in killing protestors during his father's regime.
Saif was caught in Nov. He was disguised as a Bedouin tribesman in the Sahara desert.