US President Donald Trump's administration plans to add firing squads, electrocution, and gas asphyxiation as alternative methods of executing people convicted of the gravest federal crimes, it announced on Friday, noting difficulties in obtaining drugs for lethal injections.

The recommendation came in a Justice Department report fulfilling Trump's promise to resume capital punishment at the federal level in his second term. In his first term, which ended in 2021, he resumed it after a 20-year gap, executing 13 federal prisoners with lethal injections in his final few months in office.

Acting Attorney General Todd Blanche, who released the report, has authorized seeking death sentences against nine people after Trump rescinded a moratorium on federal executions by his predecessor, Joe Biden, the department said.

"Among the actions taken are readopting the lethal injection protocol utilized during the first Trump Administration, expanding the protocol to include additional manners of execution such as the firing squad, and streamlining internal processes to expedite death penalty cases," it said in a statement.

In the report, Blanche instructed the Justice Department's Bureau of Prisons to modify its execution protocol "to include additional, constitutional manners of execution that are currently provided for by the law of certain states," pointing to the older methods of firing squads and electrocution, and the new gas asphyxiation method pioneered by Alabama in 2024.

"This modification will help ensure the Department is prepared to carry out lawful executions even if a specific drug is unavailable," the report said.

Biden, a Democrat, commuted the sentences of 37 of the people awaiting executions on federal death row, leaving only three men: Dzhokhar Tsarnaev, convicted in 2015 for the deadly bombing of the Boston Marathon; Dylann Roof, convicted in 2017 of killing nine worshipers at a South Carolina church; and Robert Bowers, convicted in 2023 of killing 11 people at the Tree of Life synagogue in Pittsburgh, Pennsylvania.

It can take many years for condemned prisoners to exhaust all legal avenues for challenging their death sentences, and none of the three men have yet received execution dates.

Typically, when a US state or the federal government adopts a new execution protocol, death row prisoners can mount legal challenges arguing that the new protocol violates the US Constitution's prohibition of "cruel and unusual punishments."

Such challenges have always failed at the US Supreme Court, which has never previously found an adopted execution method to be unconstitutional.

Lethal injection remains the most common method in the US, but has a higher rate of being botched than most other methods, including the single-drug protocol adopted by the federal government in 2019 using pentobarbital, a powerful barbiturate.

A few executions have been aborted as prison officials struggle to find a vein on a strapped-down prisoner. Opponents of the method say autopsies of executed people's lungs show they experienced drowning before dying from the pentobarbital, which they argue amounts to a torturous death.

Pharmaceutical companies refuse to sell their drugs that can be used in executions to prison systems, partly to comply with a European Union ban, forcing US prisons to seek out smaller, less-regulated compounding pharmacies willing to brew copies of those drugs.

This has led to several US states reviving older methods in recent years. Five states have firing squads, with Idaho set to adopt it as its primary method in July, according to the Death Penalty Information Center, a nonprofit research group in Washington.

Last year, South Carolina carried out the first execution by firing squad in the US in 15 years after Brad Sigmon, convicted of murdering his ex-girlfriend's parents, chose the method, saying he feared the state's alternatives of the electric chair or lethal injection would risk a slower and more torturous death.

In 2024, Alabama became the first state to execute someone by forcing nitrogen into their airways through a face mask, suffocating them, a method that has since been adopted by Arkansas, Louisiana, Mississippi, and Oklahoma.