The top court in Arkansas has halted two executions that were due to start a series of seven in 11 days.
The state’s Supreme Court acted hours before convicted murderers Don Davis and Bruce Ward were due to die, but the Davis decision could yet be reversed.
Their lawyers had argued they were mentally unfit to face execution and were denied proper assessment.
But there was a victory for the state when a federal court lifted an order that blocked all seven executions.
A blanket ruling made on Saturday that the executions could not go ahead because the lethal injection causes suffering has been overruled.
The unprecedented pace at which Arkansas will put the seven men to death has drawn international attention.
It is driven by the state’s desire to use a batch of drugs before it expires later this month.
But it has been condemned by critics as an inhumane “assembly line”.
What happened on Monday?
There were two rulings – in the first, the Arkansas Supreme Court stayed the executions of Davis and Ward, in a 4-3 decision. They have each spent more than 20 years on death row.
The state’s attorney general’s office said it would not appeal against the stay for Ward but it would appeal in the case of Davis, so he could yet be put to death on Monday.
Davis was served his last meal and moved to the Cummins Unit, which holds the lethal injection gurney.
In the other decision, the 8th US Circuit Court of Appeals in St Louis vacated the weekend ruling to halt all seven executions, reports the BBC.
Like many US states, Arkansas has struggled to find the drugs it needs to carry out executions. Its last was in 2005.
The state’s use of midazolam in its three-drug cocktail is controversial, because opponents of the death penalty say it is not effective at rendering the inmate unconscious.
The drug raised concerns after it was used in executions in three US states in 2014 that took longer than usual.
There are five more executions in Arkansas scheduled to happen by the end of April, so expect daily legal arguments on both sides.
The state is determined these executions be carried out, but those who have campaigned against the methods of execution will do all they can to block them.