The UN body on human rights on Tuesday said it was deeply saddened and disturbed by the death of 84-year-old rights activist Stan Swamy during his pre-trial detention.

It said UN High Commissioner for Human Rights Michelle Bachelet and the United Nations' independent experts have repeatedly raised the cases of Swamy, a Jesuit priest, and 15 other human rights defenders with the Indian government over the last three years and urged for their release from detention.

Swamy, who was arrested last year under the Unlawful Activities (Prevention) Act (UAPA) in connection with the Elgar Parishad-Maoist links case, died at a Mumbai hospital on Monday.

"We are deeply saddened and disturbed by the death of 84-year-old Father Stan Swamy, a human rights defender and Jesuit priest, in Mumbai yesterday, following his arrest in October 2020 under India's Unlawful Activities (Prevention) Act," Liz Throssell, the spokesperson for the UN High Commissioner for Human Rights, said.

"Father Stan had been held in pre-trial detention without bail since his arrest, charged with terrorism-related offences in relation to demonstrations that date back to 2018," she said in a statement.

Throssell said Swamy was a long-standing activist, particularly on the rights of indigenous people and other marginalised groups.

"High Commissioner Michelle Bachelet and the UN's independent experts have repeatedly raised the cases of Father Stan and 15 other human rights defenders associated with the same events with the government of India over the past three years and urged their release from pre-trial detention," she said.

"The High Commissioner has also raised concerns over the use of the UAPA in relation to human rights defenders, a law Father Stan was challenging before Indian courts days before he died," she added.