Aid workers in Libya say migrants are enduring dire conditions in detention following a wave of arrests by government security forces.
The Doctors Without Borders agency said its staff had seen cells so over-crowded that men were being forced to stand. Some said they hadn't eaten for days.
At another site the aid workers witnessed an escape attempt that was met with extreme violence.
At least 5,000 migrants have been detained in the capital, Tripoli in recent days.
There have been reports of beatings, sexual violence and one death.
The authorities say the operation has targeted illegal immigration and drug trafficking.
War crimes committed across Libya - UN report
BBC News, Geneva
A report from the UN’s first-ever fact finding mission to Libya has concluded that violations which could amount to war crimes and crimes against humanity are being committed across the country.
The report accuses all parties to the conflict there of major violations - including other countries, foreign fighters and mercenaries.
Libya has been in conflict since the fall of Muammar Gaddafi in 2011, and a UN-backed peace process has run into obstacles amid disagreement over voting rules.
The UN report depicts a country which has suffered a decade of violent chaos.
Dozens of different armed groups battling for control of Libya have attacked schools, hospitals and homes with no regard to the lives of civilians.
Migrants and refugees from sub-Saharan Africa are subjected to violent abuse that could amount to crimes against humanity.
The report also describes horrific conditions in secret prisons, in which detainees are tortured on a daily basis.
The UN investigators reviewed hundreds of documents and interviewed over 150 people in Libya, Tunisia and Italy.
They have compiled a confidential list of those responsible for the most serious violations.
Although the report concludes that, with the agreement of a ceasefire and the installation of a government of national unity, Libya has become more stable in recent months, the human rights situation remains concerning.
The UN investigators want their mandate renewed for another year.
Hundreds of Europe-bound migrants intercepted off Libya
More than 500
migrants attempting to get to Europe were on Sunday intercepted off the Libyan
coast as the country continues a massive crackdown on migrants.
The migrants were intercepted by the Libyan Coast Guard while on boats believed to heading to Europe.
hundred were crammed in one boat, while a second rubber boat with 50 people
was intercepted after its engine failed at sea.
The UN refugee agency says
majority of the people are from Bangladesh, Somalia, Sudan and Syria.
It comes just days after one person was killed and dozens injured during a police operation in an area in west Libya popular with asylum seekers and migrants.
Thousands of people have been arrested since the operation began.
The UN has condemned what it called excessive use of force against the asylum seekers.
At least 4,000 migrants have so far been arrested in the
sweeping operation mainly in the Gargaresh area of Tripoli.
North African country, in chaos since its 2011 revolution, is one of the main
departure points for migrants, mainly from sub-Saharan Africa, hoping to reach
France slashes visa numbers for North Africans
BBC World Service
France is slashing the number of visas issued to people from Algeria, Libya, and Morocco.
A government spokesman, Gabriel Attal, told Europe 1 radio that it was a drastic and unprecedented decision, made necessary by the refusal of the North African countries to take back nationals that France doesn’t want and can't keep.
He said “there was dialogue, then there were threats, and today we're carrying out those threats".
Immigration is likely to be a key issue in next year’s presidential election.
President Emmanuel Macron is widely expected to face off again against the anti-immigration far-right leader, Marine Le Pen.
Gen Haftar to drop military role ahead of Libya poll
BBC World Service
Getty ImagesCopyright: Getty Images
The Libyan commander, Khalifa Haftar, has taken a step that may enable him to run in a presidential election, due to take place in December.
General Haftar says he's stepping down from his military duties. He appears to be taking advantage of a controversial new law.
It says officials must relinquish their posts in order to stand in the elections, but it guarantees that they can return to their old positions if they lose.
The law - which was ratified by an ally of General Haftar - has been rejected by his opponents.
Analysts say gathering tensions between rival camps have put the holding of Libya's elections in doubt.
Libyan water cut as gunmen demand prisoner's release
BBC World Service
parts of west and south-western Libya are without water after armed men
demanding the release of a former henchman of Muammar Gaddafi threatened to sabotage
the water supply.
authority that runs the Great Man-Made River - which supplies fresh water
across the country - said it had suspended its flow to the region as a
precaution after gunmen entered its operational centre.
said they would blow up the main water supply if Abdullah al-Senussi - who was
the late Libyan leader's intelligence chief and brother-in-law - was not freed.
He is in jail in Tripoli and was
sentenced to death in 2015, four years after the uprising in which Gaddafi was
Great Man-Made River has been described as the biggest irrigation project in
It is a vast network of underground pipelines which brings fresh water from aquifers deep in the Sahara Desert to Libya’s coast.
The UN has launched a fresh round of talks at which delegates from across Libya will try to agree arrangements for crucially important elections.
The aim is to settle on a constitutional framework that would govern parliamentary and presidential polls scheduled for December.
The delegates failed to reach a deal at similar talks six weeks ago.
After years of war, an interim government has been installed that's meant to lead Libya into the elections.
But the failure to reach agreement so far on issues in the run-up to the polls is raising doubts as to whether they'll go ahead as planned.
Russian mercenaries support Libya anti-government troops
BBC World Service
A BBC investigation has found evidence Russian mercenaries have been operating in support of anti-government forces in Libya, in defiance of a UN ceasefire agreement.
Data from a tablet computer left by a Russian fighter indicates members of the Wagner mercenary organisation murdered civilians and subjected others to forced labour; actions which may amount to war crimes.
The findings were supported by interviews with Libyans caught up in the conflict.
Speaking to the BBC on condition of anonymity, one former Wagner employee said there were no clear rules and no documents regulating relations with the local population.
The service records of Wagner mercenaries also highlight the group's involvement in other conflicts including Syria and Ukraine.