The UN has said an airstrike that killed 44 migrants in a detention centre in Tripoli may be a war crime, as rights groups criticised the EU policy of pushing migrants back to Libya where a civil war rages around them.

Libya’s Tripoli-based government said it believed the airstrike was carried out by an Arab state backing the warlord General Khalifa Haftar, whose forces have been besieging the Libyan capital for the last three months.

Fathi Bashagha, the interior minister, did not accuse any specific country but both Egypt and the UAE are believed to have carried out air raids in support of Gen Haftar’s forces.

There was no immediate comment from Gen Haftar or his Arab backers and no one has claimed responsibility for the strike.

The UN refugee agency called for an immediate halt to the policy of returning migrants to Libya when they try to cross the Mediterranean to Europe - a policy the EU has supported by backing Libyan coast guard militias.