Amnesty International says there was a surge in the number of executions carried out worldwide in 2011, mainly centred in the Middle East.
In an annual report, the group said Iraq, Iran and Saudi Arabia were most responsible for the increase.
But it also noted that China executed more people than the rest of the world put together.
Overall however, fewer countries now practise the death penalty, the group noted.
It said the number of countries using capital punishment has fallen by a third, compared to a decade ago.
"Only 20 countries are known to have carried out executions which means that 178 are not carrying out executions," Amnesty's general secretary Salil Shetty told the BBC.
According to the review released on Tuesday, at least 676 people were executed in 20 countries in 2011, according to Amnesty, compared with 527 in 23 countries in 2010.
Amnesty no longer publishes figures for China, where the data is considered a state secret. The rights group believes the figure to be in its thousands.
The number of confirmed executions in the Middle East rose by almost 50%, to 558, it said.
It said most were in Iran, which sent 360 people to their deaths, many of them for offences under new anti-drug laws brought in last year.
In Saudi Arabia, there were at least 82 executions compared to at least 27 the previous year, while Iraq executed at least 68 people, compared to at least one in 2010, according to Amnesty.
Meanwhile, violence in Libya, Syria and Yemen in the wake of the Arab Spring made it difficult to gain accurate information on the use of the death penalty, the report noted.
The group also condemned as "shameful" the US's use of the death penalty, noting that it was the only Western democracy to execute prisoners last year.
"The big executioners are China and Iran and then you have North Korea, Iraq, Saudi Arabia, Yemen, Somalia but very sadly... the United States of America as well," said Salil Shetty.
The US ranked fifth in the world in capital punishment, with 43 people executed last year. The figure fell slightly from 2010, when 46 people were executed.
Amnesty called on China to publish its data "to confirm their claims that various changes in law and practice have led to a significant reduction in the use of the death penalty over the last four years".
However, the group noted that China had dropped the death penalty for 13 white-collar crimes.