The US state of Georgia temporarily halted executions after the drug used for lethal injections appeared faulty.
The decision came a day after Georgia delayed for the second time the execution of Kelly Gissendaner, convicted of conspiring to murder her husband, when the execution team found that the lethal pentobarbital dose appeared cloudy.
Gissendaner's execution had already been delayed for several days because of wintry weather in the southern state.
"Out of an abundance of caution, the scheduled executions of Kelly Renee Gissendaner and Brian Keith Terrell, have been postponed while an analysis is conducted of the drugs planned for use in last night's scheduled execution of inmate Gissendaner," Georgia Department of Corrections spokeswoman Gwendolyn Hogan said.
"The sentencing courts will issue new execution orders when the department is prepared to proceed," she added in a statement.
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Georgia houses one of the country's biggest prison systems, supervising nearly 55,000 state prisoners and more than 160,000 people on probation.
Gissandaner would have become the 16th female prisoner to be executed in the US since the death penalty was reinstated nationwide in 1976, compared with 1387 men who have been put to death during that period, according to the Death Penalty Information Center.
Georgia has executed 57 prisoners since 1976, including two so far this year.
Prisoner complaints from the southern state had led to the 1972 moratorium on the death penalty, before it was re-established four years later.
