A federal judge has temporarily blocked the state of Mississippi from using two drugs in executions.

US district judge Henry T Wingate issued a temporary restraining order on Tuesday saying Mississippi officials cannot use pentobarbital or midazolam, two drugs used to render prisoners unconscious. Mississippi state law requires a three-drug process, with the sedative followed by a paralyzing agent and then a drug that stops an inmate’s heart.

Jim Craig, a lawyer for two inmates, said Wingate gave the order verbally on Tuesday in a phone conference with him and other lawyers. Wingate is supposed to issue a written order, but while an online court docket reflects Wingate made the temporary restraining order, no written copy was yet available late Tuesday.

Grace Simmons Fisher, a spokeswoman for the Mississippi department of corrections, wrote in an email that the state prison system acknowledged that the order bars the state from using any drug to execute a condemned inmate. The state has filed a notice of appeal.

The state attorney general, Jim Hood, and a spokeswoman did not immediately respond to requests for comment.

Mississippi is one of a number of states facing legal challenges to lethal injections. The state has been involved in a series of disputes even as it has sought to execute one of Craig’s clients, Richard Jordan. Hood’s office had asked the state supreme court to set a 27 August execution date for Jordan, one of the plaintiffs in the suit. Jordan was convicted of capital murder committed in the course of kidnapping Edwina Marta in Harrison County in 1976.

Prisoners say they face risks of excruciating pain during an execution and that that violates the US constitution’s eighth amendment prohibition against cruel and unusual punishment.

The suit says there is no guarantee that Mississippi can mix a safe and effective anesthetic to knock out prisoners, and even then, prisoners could remain conscious during execution.

As the case was proceeding, Hood’s office told Wingate that Mississippi was abandoning its plans to use pentobarbital and instead would use midazolam. The second drug’s use has been ruled constitutional for use in executions in some states. Mississippi officials have said they have struggled to buy pentobarbital as death penalty opponents pressure manufacturers to cut off the supply of that drug.

Now 68, Jordan is the oldest inmate on Mississippi’s death row, having won three successful appeals only to be resentenced to death. He is also the longest serving, having spent 38 years on death row.

Craig has also been involved in a series of legal disputes claiming the prison system is breaking the state public records law by refusing to release documents relating to its efforts to procure execution drugs.

The last person that Mississippi executed was Gary Simmons in June 2012.