The assurance came after Amnesty concluded its first visit to Libya in 15 years, which included a meeting with President Muammar al-Qadhafi.
Amnesty believes it is the first major human rights group to hold a research mission in the North African country since its last visit in 1989, as Libya continues its efforts to rejoin the international community.
Four Amnesty delegates spent two weeks in the country and returned on Sunday.
Amnesty said it had called for the immediate release of political prisoners and the launch of an independent investigation into people who had disappeared in and outside Libya.
Although the team was able to visit prisoners, Amnesty expressed concern about the lengthy detention of defendants, particularly by the domestic security services, which it said violated Libyan law and international norms.
"Libya has been in the process of opening up for some time. They have taken a positive step in the human rights arena, though this has been limited. It is going to have to be serious engagement and serious change"
"We are pleased with the unprecedented access we were given to the Libyan authorities and others, particularly to prisoners," said Claudio Cordone, who headed the Amnesty delegation.
The group intends to publish a report based on its findings shortly, but said despite the positive reaction of the Libyans to the visit, there was still much work to be done.
"Libya has been in the process of opening up for some time," said Sara Hamud, Amnesty's Libya expert who was part of the delegation.
"They have taken a positive step in the human rights arena, though this has been limited. It is going to have to be serious engagement and serious change."
The visit comes a few months after Libya took repsonsibilty for the downing of an American airliner over Scotland in 1988.
And in December Libya also agreed to abandon its weapons of mass destruction programmes, in a move that was welcomed by the international community.