South African President Jacob Zuma is in Libya's capital, Tripoli, for talks with Col Muammar Gaddafi to seek a diplomatic solution to the conflict.
A spokesman said Mr Zuma's aim was a ceasefire and denied he would discuss exit strategies with the Libyan leader.
Government officials insist Col Gaddafi has no intention of stepping down or leaving Libya, as the rebels demand.
Meanwhile, another eight senior Libyan army officers have defected to the rebels.
The eight, including five generals, appeared at a news conference in Rome organised by the Italian government.
The rebels say a total of 120 soldiers have defected in recent days.
Since the start of the uprising in February dozens of army officers, government ministers, and diplomats have abandoned Col Gaddafi.
As Mr Zuma arrived at Tripoli's airport on Monday, children waved Libyan flags chanting "We want Gaddafi", the Reuters news agency reports.
Col Gaddafi - who was last seen on state television meeting tribal leaders on 11 May - was not among the dignitaries who greeted him.
The president was later taken to Col Gaddafi's house in the Gargour area of Tripoli, where Libyan officials said his son Saif al-Arab was killed in a Nato strike in late April.
Mr Zuma's office said the main objective of his visit was to discuss with Col Gaddafi an immediate ceasefire, the delivery of humanitarian aid and the implementation of reforms needed to end the crisis.
It also rejected as "misleading" reports that their talks would focus on agreeing an exit strategy for Col Gaddafi.
Nato imposed a no-fly zone in Libya and began bombing Col Gaddafi's forces in March as they threatened to overrun rebel-held parts of the country, a month after nationwide anti-government protests began.
South Africa voted for the UN Security Council resolution authorising the use of force to protect civilians in Libya despite the AU's concerns. Since then, Mr Zuma has joined other African leaders in accusing Nato of overstepping its mandate and calling for an end to the bombardment.
The BBC's Andrew North in Tripoli says some hope Mr Zuma's personal relationship with Col Gaddafi will make a deal possible.
But the prospects for this peacemaking bid look just as thin as last time, our correspondent says.
An African Union "roadmap", which was drawn up in February and called for an immediate ceasefire, was swiftly rejected by both the rebel Transitional National Council (TNC) and Nato because it did not call on Col Gaddafi to step down.
On Friday the G8 of leading industrial nations called for Col Gaddafi's departure. Russian President Dmitry Medvedev said on Saturday that the colonel no longer had the right to lead Libya.
The chairman of the Benghazi-based TNC, Mustafa Abdul Jalil, welcomed the statements, saying: "The entire world has reached a consensus that Col Gaddafi and his regime have not only lost their legitimacy but also their credibility."
But the Libyan government said it was not concerned by the G8's decisions.
"We are an African country. Any initiative outside the AU framework will be rejected," Deputy Foreign Minister Khalid Kaim said.
On Monday, rebel spokesman Guma al-Gamati told the BBC that he believed Mr Zuma's visit would make a difference as Col Gaddafi was far weaker and more isolated than he was last month.
"The people around him and the aides and people who are fighting for him are diminishing; some are deserting," he added.
Pro-Gaddafi forces, which control Tripoli and the rest of western Libya, have been targeted by Nato under the UN resolution aimed at protecting civilians.
Libyan state media said on Monday that Nato aircraft had killed 11 people at civilian and military sites in Zlitan, 50km (30 miles) west of Misrata.