AKIPRESS.COM - A US inmate died of a heart attack Tuesday more than 40 minutes after his execution was halted due to a botched lethal injection, triggering claims of torture.

The tragic end to the life of Clayton Lockett, a convicted murderer and rapist, caused Oklahoma to postpone the execution of a second inmate, AFP said.

Lockett was administered a new, untested three-drug protocol in what would have been the central state's first double execution in 80 years.

But Oklahoma Department of Corrections Director Robert Patton ordered the execution of Lockett stopped about three or four minutes after the start of the injection at 6:23 pm (2323 GMT), citing a "vein failure," a prisons spokesman said.

Lockett died of a "massive heart attack" at 7:06 pm after receiving all three drugs, spokesman Jerry Massie said.

Even though he was administered the injection, "the drugs didn't go into the system," the spokesman added.

The drugs included a sedative, an anesthetic and a lethal dose of potassium chloride.

Patton then immediately ordered a 14-day delay to the execution of Charles Warner, who had been set to be executed two hours later than Lockett.