US Defence Secretary Leon Panetta has expressed confidence in Libya's new government on a visit to the country.
He said Libya needed to unite fractious rebel groups, secure arms caches and build democratic institutions.
"This will be a long and difficult transition, but I am confident that you will succeed," he told a joint news conference with Prime Minister Abdurrahim al-Keib.
His short visit is the first by a Pentagon chief to Libya.
It follows a UN decision on Friday to lift sanctions on Libya's central bank and its investments subsidiary - which the BBC's Jon Donnison in Tripoli describes as a sign of confidence in the country's interim government.
The move cleared the way for Libya's new government to gain control of tens of billions of dollars frozen overseas, which it needs to pay public sector workers, rebuild war-torn towns and enhance its authority.
But Libya's competing factions - many of whom remain heavily armed - will want to be sure they get their share of the money, says our correspondent.
Referring to fractious rebel groups who are still a visible presence on Libya's streets two months after Col Gaddafi's death, Mr Panetta said he was confident Libya's interim authorities knew how to bring them together.
Mr Keib said uniting the rebel factions was a serious issue, and that programmes were being designed to attract "freedom fighters" to build a better future for Libya through opportunities other than carrying arms.
During his hours-long trip, the Pentagon chief is set to visit the reported graveyard of 13 US sailors killed in 1804 during a mission to destroy pirate ships in Tripoli's harbour.
The interim government in Tripoli had recently stepped up calls for the release of some $150bn (£96bn) held abroad to pay employee salaries and keep the country's basis services running.
The UN, US and UK had imposed sanctions against former leader Col Muammar Gaddafi's regime after it tried to crush the popular uprising against him.
The uprising virtually shut Libya's oil industry - the world's eighth largest - and exports only resumed in September.
Officials say they expect crude oil output to return to normal levels of around 1.6m barrels per day by the end of 2012.