The UN's Human Rights Council (HRC) has set up a commission of inquiry into Eritrea, seen as one of the world's most repressive states.
The three-member panel will report back in one year.
In a statement, the HRC condemned "widespread and systematic" human rights violations, including torture and other cruel punishments. Eritrea rejected the resolution.
Human rights groups have previously called the country a "giant prison".
Amnesty International last year said some 10,000 Eritreans had been imprisoned for political reasons since independence from Ethiopia in 1993. This was denied by the government.
Analysis: Imogen Foulkes, BBC News, Geneva
A country-specific inquiry into alleged violations is something Eritrea, and indeed many countries, desperately want to avoid.
Although the UN Human Rights Council cannot order sanctions or referral to the International Criminal Court (only the UN Security Council has such powers), its inquiries receive enormous public attention.
Recent investigations into Syria and North Korea have made headlines around the world, and human rights groups do believe the council's thorough research, its evidence-based findings, and the subsequent public "naming and shaming" can spur abusive regimes towards change.
Earlier this month, four Eritrean Catholic bishops took the rare step of publicly criticising life in the country as "desolate".
Many of the migrants who drowned off Lampedusa last year were from Eritrea.
Young men must do national service until the age of 40, prompting an estimated 3,000 to flee the country each month.
The use of conscription was also condemned by the HRC, along with restrictions on the freedom of expression, religion and peaceful assembly.
All private media have been closed down and only members of four religions - the Orthodox, Catholic and Lutheran Churches and Islam - are allowed to practise freely.