Washington (AFP) - The days of capital punishment may be numbered in the United States, with sharp reductions in new death sentences and executions carried out amid waning public support, according to a report released Wednesday.

The Death Penalty Information Center, a Washington-based nonprofit organization, said statistics point to a continued record decline in the use of killing as punishment.

"America is in the midst of a major climate change concerning capital punishment," said Robert Dunham, DPIC's executive director and the author of the report.

"Whether it's concerns about innocence, costs, and discrimination, availability of life without parole as a safe alternative, or the questionable way in which states are attempting to carry out executions, the public grows increasingly uncomfortable with the death penalty each year."

Though two-thirds of US states still allow the death penalty, this year is expected to end with 31 new death sentences, the DPIC said in a year-end report.

That would be a steep 37 percent drop even from 2015, when 49 death sentences marked a 40-year low.

Executions declined to 20 this year, the lowest number since 1991 and well below the 1999 peak of 98 executions, stoking hopes for opponents of the death penalty.

The 2016 executions would be the fewest since 1972, when the US Supreme Court declared capital punishment unconstitutional. It reinstated the death penalty four years later.

Public opinion polls measured support for capital punishment at a four-decade low this year, the report said.

Still, the possibility that the Supreme Court will once again outlaw the death penalty faded after Republican Donald Trump was elected president last month.

Trump, who takes office on January 20, is expected to fill the vacant seat on the nine-seat Supreme Court with a conservative judge, tipping the court to a conservative majority.

- 'Just five states' -

Notably "just five states" of the 31 where the death penalty is legal have executed a prisoner this year, the report said.

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Georgia led with nine executions, followed by Texas with seven, Alabama with two, and Florida and Missouri with one each.

For the first time in more than 40 years, no state reached 10 executions. And it was 1983 when such a small number of states carried out executions.

From 2015 to 2016, the number of executions dropped 29 percent due to a confluence of factors, including a shortage of the drugs used in executions and prolonged appeals processes.

Still, the November 8 election showed continued divisions on public views on capital punishment.

In state referendums, voters in three states -- California, Nebraska and Oklahoma -- approved measures to keep capital punishment.

But over the course of the year, abolitionists scored court victories, such as in Florida and Delaware, where death penalty statutes were declared unconstitutional.

And, in several states, Americans elected governors, judges and prosecutors known more for their defense of human rights than their support for the death penalty.

"This year's events signal a continuation of the United States's movement away from the death penalty," the DPIC report concluded.

"As the public grows increasingly skeptical of capital punishment and courts strike down outlier practices that have inflated the numbers of executions and death sentences, the death penalty's failures become ever more evident."

In this context, 2017 promises to bring highly charged issues to the fore, including questions over what constitutes the humane execution of prisoners.

At least two states, Ohio and Virginia, are planning to carry out death sentences by using midazolam, a drug that acts as a sedative but is not an anesthetic.

"In executions, midazolam is intended to put the prisoner under anesthesia, which it's not an appropriate drug to do," Megan McCracken, a leading lethal injection expert at Berkeley Law School, told AFP.

"We have seen in several executions that prisoners who are given midazolam subsequently either remain conscious or regain consciousness and struggle, gasp, and show signs of pain and suffering," she said.