The discussions are taking place via intermediaries, and Saif's whereabouts remain unknown.
The court has learnt that mercenaries have offered to help him flee to an African country that does not recognize the ICC's authority, according to Moreno Ocampo.
More from GlobalPost: Gaddafi's killer will be prosecuted: NTC officials
Prosecutors believe they have a "strong case" against Saif for crimes against humanity, Moreno Ocampo said, but stressed that he would be presumed innocent until proven guilty in a fair trial.
Libya's National Transitional Council indicated Wednesday that Saif al-Islam was considering surrendering to the court.
In a statement Friday, Moreno Ocampo said prosecutors were also prepared for the possibility that Saif would not hand himself over:
"The office of the prosecutor is also exploring the possibility to intercept any plane within the air space of a state party in order to make an arrest."
The ICC will not offer Saif any deals for turning himself in, the chief prosecutor added.
More from GlobalPost: Gaddafi's sons play hide and seek
The ICC issued a warrant for Muammar Gaddafi's son and presumed successor in June, reports the BBC.
Saif al-Islam has been in hiding for several months since then.
Recent reports had him headed for Niger, but, as Reuters points out, Niger has agreed to extradite any suspect wanted by the ICC. There has been speculation that he will try to flee to Zimbabwe: the country is not an ICC signatory and its President Robert Mugabe was a former ally of Muammar Gaddafi.
Highlights of GlobalPost's coverage of Gaddafi's capture