The US state of Utah has passed a bill that would make it the only state to allow firing squads to carry out death sentences.

The vote comes after a national shortage of the drug used for lethal injections.

The bill would permit death by firing squad - but only if the lethal injection was unavailable.

Opponents say the method is 'a relic of a more barbaric past'.

NBC News reports there are a handful of inmates on Utah's death row who can already choose firing squad as their execution method, because they were sentenced before 2004 when the state took that option away.

Utah is one of several states that have turned to alternate execution procedures because drug firms have stopped selling products to prisons for capital punishment.

Tennessee brought back the electric chair as a backup last year, but inmates have sued to stop it from being used.

It is believed a raft of executions across the country are now on hold either because the states cannot find the drugs.