Tokyo - Two detainees at an immigration centre in Japan died over the weekend, an official said on Monday, just months after the death of another man at the same facility.
An Iranian man in his 30s choked on his dinner on Friday, a spokesperson at the immigration centre in Ushiku, northeast of Tokyo, told AFP, adding that he was taken to hospital but died on Saturday afternoon.
On Sunday morning a Cameroonian man in his 40s was found unconscious in his cell, she said.
"Officials immediately called an ambulance while giving him cardiac massage," she said, adding he was pronounced dead at hospital about an hour later.
She said the Cameroonian had complained of feeling sick on Thursday, and had been moved from a shared room to a private one. She said he had also seen a doctor.
"The cause of his death is not yet known," she said, adding a autopsy will be carried out on the bodies of both men.
Rights activists say conditions in Japanese detention centres are poor and allegations of mistreatment are rife.
In October last year, an asylum-seeker - a member of Myanmar's Rohingya ethnic group - collapsed and died after staff at the Ushiku immigration centre failed to call for a medic, allegedly because the doctor was having lunch.
Kimiko Tanaka, a member of a local pressure group, said information was currently hazy, but that campaigners were trying to collect information on both cases.
"We hear that detainees, including roommates of the Cameroonian man, refused to return to their cells, which are locked at night, as a form of protest," she told AFP.
The centre's spokesperson said there had been some disquiet over the man's death, but "things have now returned to normal".
Japan tightly restricts the number of immigrants and asylum-seekers it accepts.
According to Justice Ministry figures for 2013, 3 260 people applied for asylum, many from Turkey, Nepal and Myanmar, as well as countries in South Asia and Africa.
Japan accepted six refugees during the year, down from 18 in the previous year.