The governor of Oklahoma has signed a law allowing death row prisoners to be executed with nitrogen gas.

The nitrogen, which starves the body of oxygen, replaces the electric chair as a backup to lethal injections.

Oklahoma's executions are on hold while the U.S. Supreme Court decides whether the drugs it uses are too cruel.

It’s become the first US state to approve nitrogen gas for executions under a measure Governor Mary Fallin signed into law Friday.

The law provides an alternative death penalty method if lethal injections aren’t possible, either because of a court ruling or a drug shortage.

Supporters of the new law maintain nitrogen-induced hypoxia is a humane and painless method of execution that requires no medical expertise to perform.

Fallin said in a statement: “Oklahoma executes murderers whose crimes are especially heinous.

“I support that policy, and I believe capital punishment must be performed effectively and without cruelty.
The bill I signed today gives the state of Oklahoma another death penalty option that meets that standard.”

The bill authored by Republican representative Mike Christian and Republican senator Anthony Sykes had passed the state house on an 85-10 vote and cleared the senate on a 41-0 vote.