ROME, May 5 (Xinhua) -- Italian prosecutors have launched an investigation into the deaths of eight hospital patients who died after mistakenly being given poisonous gas, a local newspaper reported Friday.

    The accident happened in a newly-opened intensive care unit at the Castellaneta hospital in the city of Taranto, in south east Italy. The unit was shut down on Friday, the local Corriere della Sera newspaper said.

    The investigators discovered that nitrogen protoxide was probably pumped into the latest victim's lungs instead of oxygen, since the respiratory equipment in the unit was confirmed as defective, the report added.

    "The only plausible explanation we can provide is that there could have been a switch in the derivation of the pipes, so that rather than being connected to oxygen they were connected to nitrogen protoxide," said Dr. Cosimo Turi, health director of the hospital.

    The presence of the anesthesia in the oxygen tubes was caused by an erroneous connection of the pipes when the structure was built, said Marco Urago, head of the local health department.

    Prosecutors suspect that seven previous patients probably died from the same cause in the past two weeks, but Turi said it was not clear if the gas problem was to blame or not.

    "We absolutely cannot define now how many and which of these deaths were attributed to the location of the gas," he said.

    In the other cases involving elderly patients with much more serious heart problems, those deaths were believed to have been natural, the hospital's coronary chief, Dr. Antonio Scarcia, was quoted as saying.

    Police inspections highlighted serious violations at one in six Italian hospitals in January, such as rat droppings on the premises and expired medicine stocks.

    Health Minister Livia Turco called for a speedy investigation and promised to collaborate with local and regional authorities, saying that she is sure that they will learn the truth quickly.

    Meanwhile, Premier Romano Prodi also called for a full investigation into the case, while urging the public not to forget that there is also quality health care in Italy, the ANSA news agency reported.