(ANSAmed) - TRIPOLI, AUGUST 27 - The Libyan capital's zoo is being used as an immigrant detention centre-prison. Though currently closed to the public, it still contains animals as well. According to a recent reportage by Libya Herald, next to the animal cages is a cement building with doors and windows bearing steel bars across them. The foreigners are held up to 72 hours in the facilities, said the commander of a militia tasked with checking the immigrants' paperwork. If they have a valid passport, visa and health certificate, the immigrants are released, while otherwise they are transferred to detention centers and held indefinitely or expelled. The unit tasked with checking immigrants detains dozens of people every day, with over 5,000 arrested in the past four months - most of whom from Sub-Saharan Africa, Tunisia and Morocco. Once in the zoo, the detainees undergo blood tests, said Al-Gerjame, the head of the zoo's irregular immigration unit, to make sure that they do not suffer from any illness. Al Gerjame said that some 20% of the immigrants test positive for either HIV or hepatitis. ''If they are ill, they will be transferred outside Libya,'' he said, '' if there is no illness, and they have visas, they can stay here and work and pay taxes.'' Amnesty International recently called conditions in the country's detention centres, where irregular immigrants including children are held indefinitely ''deplorable'', calling on the Libya government to put an immediate end to the practice of indefinite detention for immigration control. The UNHCR recently described the situation in these centres as precarious, underscoring that most of the time the hygienic conditions are very poor and there is a high risk of infection and disease contagion. (ANSAmed).