The top U.N. envoy to Libya warned Tuesday that the country faces urgent challenges as it struggles to instill democracy after decades of dictatorship, including growing political polarization, weak institutions that can't deal with escalating security problems and thousands of conflict-related detainees waiting to be charged or released.

Tarek Mitri told the U.N. Security Council that nearly two years after the ouster of longtime dictator Moammar Gadhafi, "the Libyan people will continue to endure for the foreseeable future the heavy legacy bequeathed to them over decades of brutal rule."

But Mitri added that "Libyans have not lost confidence" and remain unwavering in their commitment to building a modern and democratic state.

The Libyan government is trying to rebuild its security forces and reign in militias, many of which were born out of rebel groups that fought Gadhafi's forces. But two deadly incidents in Benghazi this month have underscored the government's failure to clamp down on the proliferation of weapons and the powerful militias following the eight-month civil war that ousted Gadhafi in August 2011.

Mitri said the government decided to create a National Guard this month which would incorporate armed brigades, "but differences on the status of revolutionary brigades and their relationship with the state remain unresolved."

He warned that a law adopted May 5 requiring the exclusion from public office of Libyans associated with the Gadhafi regime and those who committed human rights violations falls short of international standards and will have "far-reaching repercussions on the political process and the public administration." Many criteria for exclusion are arbitrary, far-reaching and vague and are likely to violate the civil and political rights of large numbers of individuals, he said.

A week before the vote, a number of revolutionary groups laid siege to several government ministries in an attempt to force through the adoption of the law. Mitri said this "set a dangerous precedent in its resort to the use of military force in order to extract political concessions."

Mitri said between 7,000 and 8,000 people detained during the civil war are still waiting to be charged or released, and "in a number of detention centers, we have observed cases of torture."

"There is also evidence of deaths in custody due to torture," he said, citing between seven and nine cases where excessive use of torture likely led to deaths.

Mitri also cited the plight of those who fled their homes during the war and are still displaced, including some 35,000 residents of the town of Tawergha, which had been a pro-Gadhafi stronghold, and thousands from the Mashashiya tribe, which also benefited from Gadhafi's rule.

Mitri urged Libya to start a national political dialogue aimed at reaching consensus on priorities for the transition. He said Libya also needs more international support, not just politically but with coordinated assistance in areas including border security.

Britain's U.N. Ambassador Mark Lyall Grant, the current Security Council president, told reporters there is a commitment by the international community to help Libya address its security challenges. He said at Tuesday's G-8 meeting it was announced that a number of countries would be assisting in training Libyan security forces. He said he also raised the possibility of a Security Council trip to Libya later this year.