A number of 25 persons were found dead on an immigration boat carrying some 300 people from North Africa to Italy, according to local media report on Monday. After receiving an SOS signal, two patrol boats sent by Italian Coast Guard Sunday night reached the immigration boat sailing from Libya about 35 miles off the coast of Lampedusa, Italy's most southern island, said local news agency Adnkronos. A number of 271 people, whose origin is still unknown, were found alive on board when the 15-meter-long ship was rescued, including 36 women and 21 children. Then after the transshipment of the people onto patrol boats, the Coast Guard found 25 bodies at the bottom of the boat, all males and mostly young. Medical clinic on the island believed that asphyxiation caused the death of the 25 people. Pietro Bartolo, a local doctor who has done an inspection on the bodies, was quoted as saying that probably the victims were dead a few hours after the start of the trip because they were all crammed into the bottom part of the boat where very little oxygen was available; in the meantime exhaust gas from the engine of the boat further "poisoned" the space. Local prosecutors have opened an investigation to reconstruct precisely the cause of the deaths. Since the onset of the Mideast and North Africa unrest in January, Lampedusa has become a key transit point for refugees fleeing that region, with the arrival of some 30,000 immigrants and refugees, mostly from Tunisia, Libya and sub-Saharan Africa since then, according to Italian official statistics.