Oklahoma inmate Clayton Lockett apparently called out during his execution, saying "something's wrong", an Associated Press reporter on the scene has said.
Lockett later died of a heart attack, but the execution of fellow inmate Charles Warner has been postponed for 14 days.
Prison director called the execution because Lockett was still moving. At 6:37 Lockett, still moving, said "somthing's wrong."
He was conscious and blinking, licking his lips even after the process began. He then began to seize.
More top news
Charlie Gard will "inevitably" die shortly after being moved to a hospice and having life-support treatment withdrawn.
Cody-Anne Jackson, who made a "sham" 999 call, several hours after suffocating Macey Hogan, will serve at least 16 years in jail.
French firefighters have tamed one of the fiercest blazes to break out during four days of wildfires in the country's Mediterranean coast.