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Despite a decline in the number of U.S. executions, America is one of the top five death-penalty purveyors in the world — behind China, Iran, Pakistan and Saudi Arabia, a new report says.

Amnesty International, which campaigns against capital punishment, tallied the number of people put to death for crimes across the globe last year and found it reached a 25-year high, even as more nations abolished executions.

"2015 was a year of extremes," Salil Shetty, secretary-general of Amnesty International, said in the report.

The human-rights group was able to confirm 1,634 executions worldwide, but that doesn't include China, which it says has a higher number than any other country but shrouds the stats as a state secret.

Nearly 90 percent of the confirmed deaths were in three countries:

Iran, which had 977 executions and where drug-traffickers are most commonly sent to the gallows

Pakistan, which notched 320 after ending a seven-year moratorium as part of a terrorism crackdown

Saudi Arabia, which executed 158 people, many with beheading, and is on pace to break that record in 2016

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The concentration helps to explain how the United States — which had 28 executions last year, a fraction of countries ranked higher — made it into the top five.

But even though fewer American states are carrying out the death penalty and the pace has slowed in those that are, the U.S. still killed more prisoners last year than either Egypt at 22 or Somalia at 25.

"As long as the U.S. continues to have executions, it's going to be part of those few countries," said James Clark, a senior death penalty campaigner for Amnesty International USA.

Executions are dropping in the U.S. largely because of legal and logistical challenges.

Family members of Shafqat Hussain, who was convicted and hanged for killing a boy, look at his dead body in Muzaffarabad, Pakistani Kashmir on Aug. 5, 2015. M.D. Mughal / AP

Many states can't buy the drugs needed for lethal injections because pharmaceutical companies have stopped selling them to prisons, often under pressure from abolitionists, and new protocols have been held up by litigation and bungles.

Nebraska repealed its death penalty statute last year, and the governors of Oregon, Colorado and Washington have imposed moratoriums in recent years.

Globally, four countries — Madagascar, Fiji, Republic of Congo and Suriname — got rid of capital punishment in 2015. That means, for the first time, a majority of countries are abolitionist.

On the other hand, executions were up significantly in Pakistan, Iran and Saudi Arabia. The activist group Reprieve said the kingdom is on pace to kill even more prisoners in 2016 and it wants Britain and the U.S. to pressure Saudi leaders to release several inmates who were sentenced to death for crimes committed as juveniles.

Supporters of Shi'ite cleric Moqtada al-Sadr burn an effigy of King Salman of Saudi Arabia during a demonstration against the execution of Shi'ite Muslim cleric Nimr al-Nimr in Saudi Arabia, in Baghdad, Iraq on Jan. 4, 2016.

"Now more than ever, the U.S. and European countries must speak out about these grave abuses being committed by our allies — including mass trials, torture, and death sentences handed down to political protesters and juveniles," said Maya Foa, head of the death penalty team at Reprieve.

In January, Saudi Arabia executed 47 prisoners in a single day, including a prominent Shiite cleric responsible for anti-government protests. The execution, based on terrorism charges, which stoked long-running tensions with Iran, a Shiite theocracy.