A US murderer sentenced to death has died nearly two hours after his execution started.

Lawyers for Joseph Rudolph Wood had filed an emergency appeal in federal court during the Wednesday execution demanding it be stopped.

The appeal said Wood was “gasping and snorting for more than an hour”.

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Attorney-General Tom Horne’s office says Wood was pronounced dead at 3.49pm, an hour and 57 minutes after the execution started.

Arizona Department of Corrections is yet to comment.

An Associated Press reporter witnessed the execution but could not immediately communicate with anyone outside the state prison in Florence where the execution took place.

The execution came after the US Supreme Court denied several appeals seeking details about the state’s execution methods.

There have been several controversial executions recently, including that of an Ohio inmate in January who snorted and gasped during the 26 minutes it took him to die.