Japan's new government is under pressure to abolish the death penalty after the human rights group Amnesty claimed the country's death row inmates are being driven insane and exposed to "cruel, inhuman and degrading" treatment.

An Amnesty report said the practice of telling inmates they are to be hanged just hours before they are taken to the gallows causes "significant mental illness". The charity called for an immediate halt to executions.

"Each day could be their last, and the arrival of a prison officer with a death warrant would signal their execution within hours," the report said. "Some live like this year after year, sometimes for decades."

The 72-page report, based on medical reports and interviews with the inmates' relatives and lawyers, says the men's families are told only after the sentence has been carried out.

Among the prisoners singled out by the report is Iwao Hakamada, a former professional boxer who has spent 41 years on death row – thought to be longer than any other condemned inmate in the world.

Hakamada, who was found guilty in 1968 of the murder of four members of the same family, was interrogated for 20 days without access to a lawyer and eventually convicted on the basis of a signed confession.

Serious doubts persist over the evidence presented against the 73-year-old, who says he was forced to sign. One of the three judges who heard his case has since said he believes the conviction is unsafe.

During a short medical assessment three years ago, Hakamada was asked if he understood what an execution was. He replied: "The wisdom never dies ... There are lots of ladies in the world, lots of animals. Everyone is living and feeling something. Elephants, dragons. No way will I die ... I won't die." A psychiatrist said recently that he was suffering from "institutional psychosis".

"Japan's death row system is driving prisoners into the depths of mental illness but they are still being taken and hanged at only hours' notice in an utterly cruel fashion," said Kate Allen, the director of Amnesty International UK.

"The mental anguish of not knowing whether each day is to be your last on Earth is terrible enough. But Japan's justice system also sees fit to bury its death row prisoners in the most punitive regime of silence, isolation and a sheer non-existence imaginable."

Allen called on the incoming government, led by the centre-left Democratic party of Japan (DPJ), to put an immediate halt to executions.

In its manifesto, the DPJ said it would "encourage a national debate" on capital punishment, although it fell some way short of promising to join the growing number of countries to have abandoned executions.

The Amnesty report paints a distressing picture of life for death row inmates in Japan. They are not allowed to talk to other prisoners or move around their cells, except to go to the toilet.

They exercise outdoors only two or three times a week and meetings with relatives and lawyers can last as little as five minutes.

Amnesty claims that prisoners diagnosed as insane continue to be executed in violation of Japanese and international law.

Of the 32 men hanged between January 2006 and January this year, 17 were aged over 60, and five of those were in their 70s. There are currently 102 inmates on death row in Japan.