ISLAMABAD: The Supreme Court (SC) on Tuesday upheld the death penalty against a mentally ill man convicted of murder, overturning a previous appeal and a court decision staying his execution, an international rights group said.

The court dismissed Imdad Ali's appeal, saying a large proportion of prisoners suffer from mental illness and they cannot let everyone go, the Reprieve group said in a statement.

The group urged Pakistan to spare Ali, saying his execution would be a violation of both Pakistani and international laws.

Harriet McCulloch, deputy director of the death penalty team at Reprieve, said it was "indisputable that Imdad suffers from serious mental illness."

Sara Bilal, a lawyer at Justice Project Pakistan, said authorities can soon set a new date for Ali's execution. He has been on death row since he was convicted in 2001. Bilal says he has been diagnosed with schizophrenia.

Ali was due to be executed on Sept 20, after Pakistan's president rejected a clemency request, but a last-minute SC decision temporarily stayed his execution.

Bilal said she sent a new clemency petition to the president from Ali's family.

Four United Nations human rights experts have also urged Pakistan to halt the execution. Agnes Callamard, Special Rapporteur on executions; Juan E. Mendez, Special Rapporteur on torture; Monica Pinto, Special Rapporteur for judicial independence; and Dainius Puras, Special Rapporteur on the right to physical and mental health, said Ali could be executed within a week.