Saif al-Islam Gaddafi can face trial in Libya - ICC
The International Criminal Court's chief prosecutor has accepted that Muammar Gaddafi's son Saif al-Islam will be tried in Libya, not The Hague.
Luis Moreno-Ocampo said the ICC had issued an arrest warrant for Saif al-Islam on war crimes charges because Libya's justice system was not up to it.
He said this was no longer the case, but that the ICC would help.
The visit comes as a new cabinet is expected to be announced.
It will be the first step to forming an elected government. Libya's transitional authority is tasked with drafting a constitution and holding democratic elections.
Prime minister-designate Abdurrahim al-Keib said all of Libya's regions would be represented.
Mr Keib was elected prime minister by the National Transitional Council (NTC) last month.
The NTC is a coalition of rival factions that came together to oust Col Gaddafi, who was killed in his birthplace, Sirte, on 20 October.
Since Saif al-Islam was arrested on Saturday, Libya's new government has insisted that he would face a fair trial locally.
As Mr Moreno-Ocampo arrived, Libya's Justice Minister Mohammed al-Allagui said: "In a nutshell, we are not going to hand him over," reported the AFP news agency.
"In May, we requested a warrant because Libyans couldn't do justice in Libya," the ICC chief prosecutor said.
"Now, as soon as Libyans decide to do justice they could do justice and we'll help them to do it."
The ICC has also issued an arrest warrant for Col Gaddafi's spy chief Abdullah al-Sanussi, who was regarded as the late leader's right-hand man - and one of the regime's most-feared figures.
Libya's government says Mr Sanussi, a brother-in-law of Col Gaddafi, was arrested at his sister's home in the southern town of Sabha on Sunday.
Saif al-Islam had been on the run since NTC forces took Tripoli in August, six months into the uprising.
Mr Keib has promised that Saif al-Islam will receive a fair trial after concerns were raised about the possibility of ill-treatment given the killing of Col Gaddafi after his capture in Sirte.
On Monday, Mr Keib said he was finalising his cabinet with the NTC and expected to announce the line-up on Tuesday.
"We will use competence as a basic measure and this way we will be able to include all of Libya's regions," he told a news conference.
An NTC source quoted by Reuters news agency said the local military commander in the western town of Zintan, Osama al-Juwali, had been designated defence minister.
Libya's deputy UN ambassador Ibrahim Dabbashi had been named foreign minister, interim oil minister Ali Tarhouni was moved to finance and oil industry executive Hassan Ziglam was taking over the oil ministry, Reuters said, but those names have not been confirmed.
The BBC's Rana Jawad, in Tripoli, says the first test of the new government will be to successfully centralise Libya's political and military powers.
Only then will the government be able to proceed with drafting a constitution and eventually hold Libya's first democratic elections in its modern history, our correspondent says.
Col Gaddafi was overthrown and his supporters defeated after a nine-month insurgency that began in the eastern town of Benghazi and eventually swept across the rest of the country.
Militias in different areas, joined by defectors from the army, were aided by Nato forces who bombed Col Gaddafi's forces under a UN mandate to protect civilians.