Relatives of a Sri Lankan woman who died at an immigration detention facility in Japan have called for improvement of the country's system.

Two younger sisters of Wishma Sandamali, who died at the facility in Nagoya City last year, made the appeal in Tokyo on Tuesday, following UN advice.

The UN Human Rights Committee last week issued a report urging Japan to improve the way detainees are treated at immigration detention facilities.

The report said the committee is concerned about "alarming reports of suffering due to poor health conditions" at such facilities, where three detainees died between 2017 and 2021.

One of the sisters, Poornima, said the UN report let the world know how Japan's immigration authorities treat detainees. She said she wants the Japanese government to change its immigration detention system.

The other sister, Wayomi, said it is hard to believe the justice minister when he says he takes the UN advisory seriously, given that cases like her sister's have been repeated over years. She urged the Japanese government to put its words into action.

Lawyer Ibusuki Shoichi, who represents the relatives, said the UN advisory alone may not change Japan's system, but reform could begin if people speak out. He said this will not be easy, but efforts should continue.

Wishma's relatives have filed a compensation lawsuit against the government, saying immigration authorities failed to provide necessary medical care despite her worsening condition.