Amnesty International has said that Iran executed 94 people in 2005, while 86 were executed in Saudi Arabia.
Iran is the only country known to have executed juveniles in 2005
Iran, the rights group said, was the only country known to have executed juvenile offenders in 2005.
At least eight people were killed for crimes committed when they were children, including two who were still under 18 at the time of execution.
Some detainees in Saudi Arabia had been tried and sentenced in a language they did not speak or read.
80% of executions in China
Iran carried out 94 executions, Saudi Arabia 86 and the US 60
2,148 people were executed in 22 countries
86 countries have abolished the death penalty, while 122 have abandoned executions
Source: Amnesty International
Others were taken from their prison cells and executed without even knowing that a death sentence had been imposed on them, the group said.
The group's annual analysis on the use of the death penalty worldwide was published on Thursday.
Trend against death penalty
Amnesty International says the trend toward abolishing the death penalty continues to grow, with the number of countries conducting executions halving over the past two decades.
The organisation's Secretary General, Irene Khan, said that as the world turned away from using the death penalty, it was a glaring anomaly that China, Saudi Arabia, Iran and the US stood out for their extreme use of this form of punishment.
China accounted for 80% of the execution in 2005. A further 14% of the executions carried out last year occurred in Iran, Saudi Arabia and the United States.
"The death penalty is the ultimate, irreversible denial of human rights because it contravenes the essence of human values," Ms Khan said.
"It is often applied in a discriminatory manner, follows unfair trials or is applied for political reasons. It can be an irreversible error when there is miscarriage of justice."