Supreme Court denies appeal from Oklahoma death row inmate
The United States Supreme Court building. (Shutterstock.com)

The US Supreme Court on Wednesday rejected an appeal by a Death Row inmate in Oklahoma who is to be executed despite claims by his lawyers that he is severely mentally ill.

Benjamin Cole, 57, is to be put to death by lethal injection at 10:00 am (1500 GMT) at the Oklahoma State Penitentiary in McAlester.

Cole was sentenced to death in 2004 for the murder of his daughter, Brianna.

He was accused of killing the crying infant to silence her so he could continue playing a video game.

According to his lawyers, Cole suffers from "debilitating mental illness" and the US Constitution prohibits the execution of someone who is not mentally competent.

Cole has been diagnosed with paranoid schizophrenia and brain damage, his lawyers said, and "his condition has deteriorated to the point that he is largely catatonic."

"(Cole) cannot manage his own basic hygiene, and crawls on the cell floor if without a wheelchair," they said in a statement.

"He barely communicates with prison staff or his own attorneys, going days at a time without speaking to anyone."

Lower courts have rejected the claims that Cole is not mentally competent and the Supreme Court denied his last-minute appeal for a stay of execution without comment.

According to the Oklahoma authorities, Cole identifies as a "Messianic Jew" and "his refusal to speak to certain individuals appeared to be a choice on his part" motivated by his "extreme religiosity."

"Cole's claim of incompetency rests on experts who have not had actual conversations with him concerning his execution," they said.

"In contrast, Cole willingly engaged with a neutral expert at a state-run hospital and very clearly expressed his rational understanding of his punishment," they said.

There have been 11 executions in the United States this year, including three in Oklahoma.