A US appeals court has halted the scheduled execution of a convicted killer in Texas hours before he was to be put to death, to see if the punishment should be suspended because the convict was intellectually disabled.

Convicted rapist and murderer Robert James Campbell was set to die Tuesday evening. He would have been the first inmate executed in the US since a botched lethal injection in Oklahoma in April raised new questions about capital punishment.

"Campbell and his attorneys have not had a fair opportunity to develop Campbell's claim of ineligibility for the death penalty. In light of the evidence we have been shown, we believe that Campbell must be given such an opportunity," a three-judge panel of the US Court of Appeals for the Fifth Circuit wrote in a decision issued on Tuesday.

Texas officials were reviewing the court's order and had no further comment, said Lauren Bean, spokeswoman for the Texas Attorney General's office.

Execution drugs

Lawyers for Campbell also asked the US Supreme Court for a stay on grounds that the problems in Oklahoma and secrecy surrounding execution drugs demand a halt to allow for a sober reflection on how the death penalty is carried out.

Campbell was set to die for killing a 20-year-old Houston bank teller, Alexandra Rendon. He was convicted along with a co-defendant of kidnapping, raping and shooting Rendon.

About two weeks ago, Oklahoma attempted to halt the execution of convicted murderer Clayton Lockett after what prison officials said was a blown vein that made them unsure if the lethal cocktail was being properly administered.

Lockett, mumbling and in apparent pain on a prison gurney with an IV in his groin, died of an apparent heart attack 43 minutes after the procedure started. The execution was the state's first using a new three-drug lethal injection mix.

The White House said the Oklahoma execution failed to meet humane standards. President Barack Obama said it raised questions about the death penalty and that he would ask the US attorney general to look into the issue.

Source: Agencies