Libyan officials are determined to resist attempts to bring Muammar Gaddafi's son, Saif al-Islam, before the international criminal court, claiming he should instead face justice at home.

Colonel Ahmed Bani, the military spokesman for Libya's interim rulers, said they were insistent that the international body should not win custody of its most wanted man. "We will not accept that our sovereignty be violated like that," he said. "We will put him on trial here. This is where he must face the consequences of what he has done. We will prove to the world that we are a civilised people with a fair justice system. Libya has its rights and its sovereignty and we will exercise them."

The gruesome scenes of his father's death give Gaddafi, 39, little incentive to surrender to the new rulers, or the rebel forces searching for him in the Sahara.

It is understood that Gaddafi has acknowledged to the ICC and the National Transitional Council that he is aware of his father's brutal demise in his hometown of Sirte. Officials in Tripoli fear that the former heir apparent does not intend to surrender to The Hague, and is playing for time in an attempt to escape into a nearby African state.

The seven-month air blockade will be lifted on Tuesday, meaning that Gaddafi, who is believed to be in the south, may no longer have to fear the Nato jets that attacked a convoy carrying his father, as he attempted to flee from Sirte.

A convoy carrying Saif was also hit by an airstrike as it began its journey south on 19 October from the desert town of Bani Walid, which he had used as a hideout since shortly after the fall of the capital. "We knew he was there, and we knew Motassim [his brother] was in Sirte," said Bani. "We intercepted a telephone call between them, and after that Saif went south." Since then, the ICC says that a go-between has been in contact, sounding out the court about Gaddafi handing himself in to face an indictment issued against him in June, which alleges that he incited people to murder during the eight-month civil war.

Luis Ocampo, the ICC chief prosecutor, said that a representative of Gaddafi had told the court that he would contest the serious charge against him, of committing crimes against humanity, and that he would be proved innocent.

Bani said that the NTC believed Gaddafi was being protected by mercenaries who also helped evacuate two of his brothers, as well as his sister and mother, to Algeria in August, and who tried to aid his father's ill-fated escape from Sirte. "They are organised and clearly professional," he said. "We don't know who they are, but we suspect they are foreigners."

Libya's fledgling civilian leadership has repeatedly sought assurances from the governments of Mali and Niger that neither state would offer Saif Gaddafi refuge. However, another son, Saadi, is known to have crossed into Niger in September, where he remains under regime protection.

Saadi Gaddafi is not considered to have played a pivotal role in the crackdown against anti-regime demonstrations in Benghazi in February, which led to the armed insurrection. However, at the time Muammar Gaddafi sent Saadi to Benghazi to assess the situation and command elite forces.

Meanwhile, at the scene of the initial February uprising, the courthouse on Benghazi's foreshore, a black flag identical to that used by al-Qaida was recently raised next to the new Libyan flag. It continued to fly on Saturday, despite the concerns of some residents.

Bani said that he has seen reports of the flag, which represents a claim by fundamentalist Islamists for a stake in post-Gaddafi Libya. He declined to comment ,saying a response should come from the civilian leadership. In his last interview before the fall of Tripoli, Saif Gaddafi had suggested that radical Islamists would vie for a prominent role in the absence of strongman ruler. However, he had also suggested that he had won the support of Islamic rebels from eastern Libya, whom the Gaddafi regime had viewed as subversive threats through much of its 42 years in power. Those claims of Saif Gaddafi now seem tenuous, with Islamists throughout Libya determined to capture the remnants of the Gaddafi regime before they can flee, or are extradited to face the ICC. "He is the last main piece of all of this," said Ibrahim Beit al-Mal, the commander of the Misrata military council. "But where he is, is a mystery. After Bani Walid he vanished."

Without Nato air cover, intercepting the fugitive's convoy in southern Libya would be extremely difficult for Libyan forces. What remains of Colonel Gaddafi's air force is not known, and, in any event, the porous border with Niger could serve as a sanctuary if Saif Gaddafi is able to secure the support of the Tuareg tribes, which had been supported by his father for several generations.

Officials in northern Niger last week suggested that they would be prepared to host Saif Gaddafi, who championed unity among Saharan Africans and gave hundreds of thousands work permits and residency in Libya.

After Sirte fell, large amounts of cash wrapped in plastic, along with gold bullion, were dug up from the ground near Muammar Gaddafi's last refuge. It is widely believed that his son is also carrying cash and gold that he could use to buy the support of tribesmen and fund a passage into exile in a state that does not recognise the jurisdiction of the ICC. "That is what we fear," said Bani. "Few of us think that he is serious about the ICC."