US states overnight on Tuesday carried out the first two executions since a botched one in April that caused a prisoner to suffer triggered a hot debate on lethal injection.
In Oklahoma in April, Clayton Lockett, a convicted killer and rapist, was put to death by lethal injection in a process that took 43 minutes, well over the expected time of a little over 10 minutes.
He was seen writhing in pain in a spectacle that drew widespread condemnation, even from President Barack Obama.
Since then five executions slated to take place had been delayed as states reviewed their execution procedures.
On Tuesday and early Wednesday one execution was in Georgia and the other in Missouri. Both were also by lethal injection and came after last minute appeals were rejected by the US Supreme Court.
The appeals centered on secrecy surrounding the lethal injection procedure, the origin of the drugs used and whether the people carrying out the sentences were truly qualified.
In the first of them, Marcus Wellons, 58, convicted of the 1989 kidnapping, rape and murder of a 15-year-old girl, was put to death shortly before midnight in the southern state of Georgia, a spokesman for the prison system said.
In the second case, John Winfield, 43, convicted of killing two women, was executed in the central state of Missouri, state prison system spokesman Mike O'Connell said.
A third execution was also scheduled for 6pm (2200 GMT) on Wednesday in the southern state of Florida.
In that case, John Henry, 63, is being sentenced to death for killing his wife and her five-year-old son in 1985. At the time he was out on probation over the killing of his first wife.
US states using the death penalty have faced crises over shortages of lethal injection drugs after European suppliers stopped supplying pentobarbital for use in executions.
The shortages have prompted prison departments in the 32 states that still allow the death penalty to seek new supply sources or new drug protocols.
After the botched execution in April, Oklahoma suspended the procedure for six months as it reviews its practices and probes the case of Lockett.
The new executions were the 21st and 22nd so far this year in the United States.