Story highlights Amnesty International: 1,634 people were executed in 2015

Nearly 90% of these executions took place in Iran, Pakistan and Saudi Arabia

Real number could be much higher as China doesn't divulge numbers

(CNN) The world saw the highest number of recorded executions in more than 25 years in 2015, according to a new report from human rights group Amnesty International.

In what the organization called an "alarming surge," at least 1,634 people were executed last year, an increase of more than 50% on 2014

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"The rise in executions last year is profoundly disturbing," said Salil Shetty, Amnesty International's Secretary General, in a statement.

"Not for the last 25 years have so many people been put to death by states around the world."

According to the rights group's annual report the dramatic increase was fueled by three nations -- Iran, Pakistan and Saudi Arabia -- who together were responsible for nearly 90% of executions in 2015.