Updated at 11:45 a.m. ET

A judge has blocked the U.S. government's plan to begin executing federal prisoners for the first time in nearly 20 years. U.S. District Judge Tanya S. Chutkan issued a preliminary injunction Wednesday halting four executions set to begin next month over concerns about the government's lethal injection method.

In a memorandum issued with her order, Chutkan wrote that at least one of the four death row inmates — Daniel Lewis Lee, Wesley Ira Purkey, Alfred Bourgeois and Dustin Lee Honken — was likely to succeed in his lawsuit against federal agencies.

"Plaintiffs have clearly shown that, absent injunctive relief, they will suffer the irreparable harm of being executed under a potentially unlawful procedure before their claims can be fully adjudicated," the judge wrote.

The Justice Department announced in July that it intended to resume capital punishment at the federal level.

The four convicted murderers filed their complaints later that summer, joining a long-dormant lawsuit against the Justice Department and the Federal Bureau of Prisons.

That original suit, filed in 2005 by other inmates, challenged the use of a three-drug cocktail in lethal injections. The case had been on hold since 2011, when the Obama administration effectively halted federal executions as it reviewed possible modifications to the injection protocol.

Now, the four inmates — whose complaints were consolidated into a single case before the U.S. District Court for the District of Columbia — argue that the changes announced earlier this year violate the Federal Death Penalty Act of 1994.

They say the July announcement, which outlines the use of a single drug, pentobarbital, rather than the three-drug cocktail used in many states, violates the FDPA's mandate that the federal government follow the practices of the state in which the inmate's sentence was handed down.

They've got a point, according to Chutkan.

"Given that the FDPA expressly requires the federal government to implement executions in the manner prescribed by the state of conviction," she wrote, "this court finds Plaintiffs have shown a likelihood of success on the merits as to this claim."

The Obama appointee also didn't buy the government's case for urgency.

"While the government does have a legitimate interest in the finality of criminal proceedings," Chutkan added, "the eight years that it waited to establish a new protocol undermines its arguments regarding the urgency and weight of that interest."

A fifth inmate, Lezmond Mitchell, whose execution had been scheduled for Dec. 11, obtained a stay of his own in a separate split decision last month by the 9th U.S. Circuit Court of Appeals.

The Justice Department did not immediately offer a public response to Wednesday's decision. But in a statement issued in July, U.S. Attorney General William Barr maintained that "we owe it to the victims and their families to carry forward the sentence imposed by our justice system."

Executions have been rare in recent decades, with only three inmates put to death by the U.S. government since the federal death penalty statute was effectively reinstated in 1988 — and none since 2003, according to the Bureau of Prisons.

At the state level, meanwhile, capital punishment is legal in 29 states — though there is controversy over the means with which it is carried out. Several botched executions in recent years have raised serious questions about the effectiveness of drugs used in lethal injections.

In a statement issued Wednesday after Chutkan's decision, a lawyer for the four plaintiffs on federal death row celebrated the stay.

"This decision prevents the government from evading accountability and making an end run around the courts by attempting to execute prisoners under a protocol that has never been authorized by Congress," Shawn Nolan said.

"By granting the preliminary injunction, the court has made clear that no execution should go forward while there are still so many unanswered questions about the government's newly announced execution method."

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