Amnesty International has accused Libya of a number of human rights violations, including the disappearance of prisoners, use of the death penalty, torture and intolerance of political activity.
The four-member team, given its first access to Libya in 15 years, shared its report with Libyan leader Muammar Gaddafi, who promised to consider Amnesty's recommendations, team leader Claudio Cordone said.
He said that while there have been minor improvements in Libya's human rights, the situation "remains problematic in many respects".
"We have people imprisoned solely for the peaceful expression of their views.
"We have a wide practice of holding people for years without being given access to their families and lawyers, with torture used often," Cordone said.
"We have the death penalty for a variety of offences, including some that criminalise freedom of expression. We have people's courts with unfair trails."
The Amnesty team arrived in Tripoli two weeks ago, in a visit not reported by Libyan media.
The group visited a police academy and Abu Salim prison, notorious in Libya for the inhumane conditions of its 625 political and military prisoners.
They also visited the town of Beni Waled, where several houses belonging to families of alleged political activists were demolished in October 2002.
Amnesty's recommendations included the release of political prisoners, independent investigations into the fate of missing people, a review of the death penalty and the abolition of the people's court, which deprives citizens of the right to be represented by legal counsel.
PA