Iran executed close to a thousand people in 2015 while Pakistan put to death 326 people and Saudi Arabia more than 150, and the three countries together accounted for 90 percent of recorded judicial killings last year.
Amnesty International, which relapses staggering figures that point to a dramatic rise in the number of executions worldwide, said the total number of judicial killings excluded capital punishments carried out in China, where numbers remain a state secret.
The rights organisation said 2015 saw the highest number of executions in a quarter century. The absolute numbers rose by 54 percent, with at least 573 more people killed than in 2014.
Amnesty said at least 1,634 people were executed in different countries, the highest recorded by execution total since 1989.
Methods employed by various countries included hanging, shooting, lethal injection and beheading.
The rights watchdog said the number of executions would rise sharply if numbers were available for China, where it says thousands are executed every year.
"Amnesty stopped publishing its estimated figures in 2009, challenging the Chinese government to reveal their own figures and demonstrate that they really are limiting their use of the death penalty - something they have claimed to be doing since the country's highest court began reviewing all death penalty cases in 2007. China remained the world's top executioner," the latest report says.
While four countries expunged death penalty in 2015, a total of 25 countries carried out executions in 2015, up from 22 in 2014.
Madagascar, Fiji, Suriname and Congo abolished death penalty in 2015. Mongolia has adopted a result ion to abolish judicial killing, and the law will come into effect in 2016.
In the US, Pennsylvania abolished the death penalty for all crimes bringing the total number of US states that have abolished the death penalty to 18.
At least 1,998 people were sentenced to death in 2015 and at least 20,292 prisoners remained on death row at the end of the year.
The report also says Countries, including the US, continued to flout other aspects of international law, putting to death people with mental or intellectual disabilities.
