The US government is set to carry out the death penalty for the first time in 16 years, William Barr, the attorney general, announced on Thursday, despite criticism of capital punishment as “immoral and deeply flawed”.

The justice department scheduled the execution of five death row federal inmates for December and January.

Congress has expressly authorised the death penalty through legislation adopted by the people’s representatives in both houses of Congress and signed by the president, Barr said in a statement.

He added: “Under administrations of both parties, the Department of Justice has sought the death penalty against the worst criminals, including these five murderers, each of whom was convicted by a jury of his peers after a full and fair proceeding.

“The justice department upholds the rule of law – and we owe it to the victims and their families to carry forward the sentence imposed by our justice system.”

The government has put to death only three defendants since restoring the federal death penalty in 1988, the most recent of which occurred in 2003, when Louis Jones was executed for the 1995 kidnapping, rape and murder of a young female soldier. There are about 60 people on federal death row, according to the Death Penalty Information Center (DPIC).

Thirty US states currently allow capital punishment but, in four of them, governors have issued moratoriums on the death penalty, the DPIC says. Twenty states have abolished or overturned it. New Hampshire became the latest US state to abolish the death penalty in May.

The move to execute federal death row inmates was sharply rebuked by opponents of the death penalty. Senator Kamala Harris, a former prosecutor now running for the 2020 Democratic nomination for president, tweeted: “Let me be clear: capital punishment is immoral and deeply flawed. Too many innocent people have been put to death. We need a national moratorium on the death penalty, not a resurrection.”

Another 2020 contender, Senator Cory Booker, said the move was typical of Barr’s resistance to criminal justice reform. “Throughout our nation’s history we have seen how the death penalty is not only ineffective and immoral, but also fraught with biases against people of color, low-income individuals, and those with mental illness. It is a waste of taxpayer dollars and does nothing to improve public safety.

“Instead, capital punishment seeks to satisfy a desire for vengeance and retribution. Our government must represent the best of who we are, not the worst. We can, and should, do better.”

Barr, who was appointed by Donald Trump, is Catholic. Last year Pope Francis altered the teachings of the Catholic faith to oppose the death penalty in all circumstances.

The justice department said the Federal Execution Protocol Addendum, which closely mirrors protocols currently used in Georgia, Missouri and Texas, replaces a three-drug cocktail previously used in federal executions with a single drug: pentobarbital.

It added that 14 states have used pentobarbital in more than 200 executions while federal courts, including the supreme court, have repeatedly upheld the use of pentobarbital in executions as consistent with the eighth amendment.

But Chris McDaniel, a news producer at HBO’s Last Week Tonight with John Oliver, who researched the use of lethal injection for an item on the death penalty, tweeted: “Unsaid in the press release is what kind of pentobarbital they plan on using. Manufactured pentobarbital is almost impossible for executioners to get. Compounded pentobarbital is easier to get, but raises serious concerns about its quality.”

Barr directed Hugh Hurwitz, the acting director of the Federal Bureau of Prisons, to schedule the executions of five death-row inmates convicted of murdering children and elderly people.

They are Daniel Lewis Lee, a member of a white supremacist group, who murdered a family of three, including an eight-year-old girl; Lezmond Mitchell, who killed a 63-year-old woman and her nine-year-old granddaughter; Wesley Ira Purkey, who raped and murdered a 16-year-old girl and killed an 80-year-old woman who suffered from polio; Alfred Bourgeois, who sexually molested and beat to death his two-year-old daughter; and Dustin Lee Honken, who shot and killed five people including two children.

The executions will take place in December and January at the high security US penitentiary Terre Haute in Indiana.

A recent report from the Bureau of Justice Statistics showed that at the end of 2017, 32 states and the Federal Bureau of Prisons held 2,703 prisoners under sentence of death – a decline for the 17th consecutive year.

California has more prisoners under sentence of death than any other state, with 742, followed by Florida with 349. Texas carried out more executions than any other state in 2017, with seven.

A 2014 study by researchers from Michigan and Pennsylvania found that at least 4.1% of all defendants sentenced to death in the US in the modern era are innocent.