The execution chamber at the Nevada State Prison in Carson City, Nev., is shown Thursday, March 22, 2001. Sebastian Bridges, a South African national is scheduled to be executed on Saturday, April 21, 2001 for murdering his estranged wife\'s lover outside Las Vegas in 1997. (AP Photo/Cathleen Allison)

LITTLE ROCK, Arkansas - Six death row inmates sued Arkansas state prison officials on Friday, claiming execution procedures adopted by legislators last month will put them at risk for an agonizing death.

The inmates claim the state's planned use of a slow-acting barbiturate violates their right to be killed swiftly. They asked a state judge to prevent the Department of Correction from carrying out any execution.

Lawyers for the inmates said that when their clients were convicted, Arkansas law required that they be given a “lethal quantity of an ultra-short-acting barbiturate in combination with a chemical paralytic agent until the defendant's death.”

Procedures adopted last month call for the use of an anti-anxiety drug and phen, a slow-acting barbiturate, in “a completely untried combination and quantity of drugs that will take hours to be injected and to reach their peak effect, that will produce agonizing and degrading effects during the procedure, and that will severely and permanently injure - but may not kill - the Prisoners,” the lawyers wrote.

Aaron Sadler, a spokesman for Attorney General Dustin McDaniel, says the AG's office received the lawsuit and was reviewing it.

Attorney Jeff Rosenzweig, who filed the suit, said the new law includes problems similar to the old law, such as allegedly violating separation of powers between the Legislature and the Correction Department.

The Arkansas Supreme Court tossed out the state's previous execution law, saying the Legislature had ceded too much control to Correction Department administrators in carrying out executions. Legislators this year adopted a revised law, directing that inmates be killed with a barbiturate but leaving the specifics to prison officials.

The Associated Press learned last week that the state had obtained doses of lorazepam, an anti-anxiety drug, and phenobarbital, a slow-acting barbiturate used to treat seizures, with which to kill its condemned prisoners. Prison spokeswoman Shea Wilson said phenobarbital was on a list of FDA-approved barbiturates in court papers filed by lawyers for the inmates in a previous case.

In a letter obtained by the AP this month, federal public defender Jenniffer Horan told Democratic Gov. Mike Beebe that phenobarbital takes effect more slowly than other drugs used to execute prisoners and that it carries a “substantial risk of a lingering and inhumane death.”

The Death Penalty Information Center said no state has ever used phenobarbital in an execution.

The lawsuit by the inmates - Stacey Johnson, Jack Jones, Jason McGehee, Bruce Ward, Kenneth Williams and Marcel Williams - names Correction Department Director Ray Hobbs.

Arkansas' last execution was in 2005. - Sapa-AP