Oklahoma death row prisoner Charles Warner’s execution was postponed at the last minute yesterday evening after fellow prisoner Clayton Lockett’s execution was botched.

A new drug combination left Mr Lockett writhing and clenching his teeth on his execution trolley, leading prison officials to halt the proceedings before his eventual death from a heart attack.

He was declared unconscious 10 minutes after the first of the three new drugs was administered.

However, he began breathing heavily three minutes later, writhing, clenching his teeth and straining to lift his head off the pillow.

The blinds were eventually lowered to prevent official witnesses in the viewing gallery from seeing what was happening in the death chamber and the top prison official eventually called a halt to the proceedings. 

Mr Lockett died of a heart attack a short time later, the Department of Corrections said.

“It was a horrible thing to witness. This was totally botched,” said Mr Lockett’s lawyer David Autry.

There was already controversy over the planned double execution in light of the state’s refusal to give details of new medications sourced in response to European states’ refusal of export licences for the normal poisons.

Oklahoma refuses to come clean, as do Texas and Missouri, claiming that public knowledge could open companies to political pressure. 

This was the first time Oklahoma had used midazolam as the first element of its three-drug death cocktail.

Governor Mary Fallin ordered a 14-day stay of execution for Mr Warner.