Human rights organisation Amnesty International says it believes thousands of people were executed in China last year.
It called for the government in Beijing to reveal how many prisoners it put to death, saying the exact numbers remain a state secret, the BBC reports.
In its annual worldwide report on the death penalty, Amnesty estimates China executed thousands of people in 2009, more than the rest of the world put together.
Amnesty Secretary General Claudio Cordone said most countries have now ended capital punishment, although about 714 people were known to have been executed in 18 countries in 2009.
But the group said the true global figure could be much higher, as thousands of executions were thought to have been carried out in China alone.
At least 366 people were executed in Iran, 120 in Iraq and 52 in the United States.
Amnesty praised Burundi and Togo for abolishing the death penalty in 2009 and said that for the first time in modern history, no-one had been executed in Europe or the former Soviet Union over the year.