Rights groups have called for the evacuation of detention centres where they say migrants face inhumane conditions.

An “urgent and immediate evacuation of all refugees and migrants” in Libya has been called for after a military strike on a detention centre for migrants claimed at least 53 lives.

The attack, that took place on Tuesday, also reignited a debate over the ill-treatment of the mainly African people who transit through the turbulent north African country.

The UN has called for an investigation into the attack on Tajoura detention centre which held 600 people in a suburb of the Libyan capital Tripoli, part of a global chorus condemning the attack which also injured 130 people.

The attack follows repeated warnings about the vulnerability of migrants in guardhouses close to Libya’s conflict zones, and raises tough questions about whether it was necessary to lock them up in the first place.

“This is not the first time that migrants and refugees have been caught in the crossfire, with multiple air strikes on or near detention centres across Tripoli since the conflict started in the city,” said Prince Alfani, a coordinator for the medical aid group Doctors Without Borders (known by its French initials, MSF).

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“What is needed now is not empty condemnation but the urgent and immediate evacuation of all refugees and migrants held in detention centres out of Libya.”

Human rights groups and analysts told Al Jazeera the deaths should act as a “wake up call” and help stop similar tragedies from happening in the future.

As well as calling for a war-crimes investigation, they questioned Libya’s UN-recognised government’s decision to detain thousands of non-criminal migrants and the European Union for its role in closing down transit routes across the Mediterranean Sea.

“The UN-backed Libyan government should have never placed refugees and migrants in those hangars. They shouldn’t have been detained at all – in Tajoura or elsewhere – as placing foreign nationals in arbitrary detention breaches international law,” Matteo De Bellis, a migration expert for Amnesty International told Al Jazeera.

Around 6,000 migrants and refugees are held in lockups across Libya, according to the Libyan Department for Combatting Illegal Migration (DCIM). Almost half of those are in or near Tripoli which has become the scene of intense fighting in recent weeks.

Many are detained in facilities close to conflict zones or at military bases, like the hangar in Tajoura, which again is “violation of international law”, added De Bellis.

In May, UNHCR, the UN’s refugee agency, had called for the Tajoura centre to be evacuated after a projectile landed 100 metres away, injuring two migrants. Shrapnel from that blast tore through the hangar’s roof and almost hit a child.

Migrants transiting Libya have faced arrest and detention for decades, but the NATO-backed overthrow of Muammar Gaddafi in 2011 and the country’s collapse into inter-militia violence increased the risks they faced there.

With this, an economy has developed around handling refugees and migrants that drives their exploitation and abuse, said John Dalhuisen, a regional expert with the European Stability Initiative think-tank.

“Migrants are a rich source of revenue. Detention centres form part of a chain of trafficking where everyone takes a cut: government officials, traffickers and militiamen. The roles are often hard to distinguish,” said Dalhuisen.

Libya’s mission to the UN did not respond to Al Jazeera’s request for comment.

Libya is one of the main departure points for the African migrants fleeing poverty and war who try to reach Italy by boat. But many are picked up and brought back by the Libyan coastguard, in a scheme backed by the EU.

An EU spokesperson told Al Jazeera the move was in order to stop migrants and refugees from drowning and support the Libyan coastguard’s efforts to intercept boats and “end to the cruel and inhumane business mode of the smugglers”.

“We have also pushed Libyan authorities to put in place mechanisms improving the treatment of the migrants rescued by the Libyan coastguard after their disembarkation in Libya … ensuring that migrants are properly screened and registered, assisted in accordance with their specific condition, and placed in reception centres that meet international humanitarian standards,” the spokesperson said.

‘Fig-leaf efforts’

Under a programme with the UN and the African Union, around 40,489 migrants and refugees have been helped back to their home countries, while 4,000 others have been granted protection and resettled in another country, the EU spokesperson said.

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But Judith Sunderland, an associate director for Human Rights Watch, said the EU was effectively washing its hands off the migrant problem and making Libya responsible despite the political chaos there.

“It is our view that EU policies perpetuate a cycle of extreme human-rights abuses against migrants and asylum seekers in Libya,” said Sunderland.

“Fig-leaf efforts to improve conditions and get some people out of detention do not absolve the EU of responsibility for enabling the barbaric detention system in the first place.”

The EU should take its “share of responsibility for people rescued at sea” and ensure they are not sent back “to a conflict-torn country like Libya”, according to Elinor Raikes, director for Europe and North Africa at the International Rescue Committee.

This week’s attack was the highest publicly reported toll from an air raid or shelling since eastern forces under renegade military commander Khalifa Haftar launched an offensive three months ago to take Tripoli, the base of Libya’s internationally-recognised government.

The UN Security Council started debating the crisis late on Wednesday, though it remained unclear whether it was the fault of Haftar’s self-declared Libyan National Army (LNA), the UN-recognised Tripoli-based government’s forces or another group.

UN Secretary-General Antonio Guterres was “outraged” by the “horrendous incident” and called for an “independent investigation” to prosecute those responsible for what many onlookers call a war crime, said spokesperson Stephane Dujarric.

“This incident underscores the urgency to provide all refugees and migrants with safe shelter until their asylum claims can be processed or they can be safely repatriated,” Dujarric told reporters Wednesday.

Haftar’s bid to capture Tripoli has derailed UN efforts to broker an end to the mayhem that has ravaged the hydrocarbon-producing North African country since the brutal, NATO-backed overthrow of Muammar Gaddafi in 2011.