The world's top executioner China put 2,400 people to death last year, a US-based rights group said, shedding rare light on a statistic Beijing tries to keep a state secret.

The Dui Hua Foundation said on Tuesday that the figure had gone down by 20 percent since 2012, but China is so sensitive about the issue that it has done nothing to publicise the decline in its use of the death penalty.

The foundation, a nonprofit organisation that seeks clemency and better treatment for at-risk detainees, said it obtained its figures from "a judicial official with access to the number of executions carried out each year".

"China currently executes more people every year than the rest of the world combined, but it has executed far fewer people since the power of final review of death sentences was returned to the (Supreme People's Court) in 2007," Dui

Hua said.

China's top court examines all death sentences issued in the country, and sent back 39 percent of those it reviewed last year to lower courts for additional evidence, Dui Hua added, citing a report by the Southern Weekly newspaper.

Amnesty International releases annual reports of death penalties in 22 countries. Its 2013 report recorded an increase of 14 percent in executions worldwide from the 2012 figure.

Amnesty has not published statistics on China's death penalties since 2009 due to the difficulty of getting information.

Amnesty's overall figure in 2013 for death penalties carried out worldwide was 778, which means that if the 2,400 figure is accurate, China executed more than three times the number of people than every other country combined.

Iran, Iraq, Saudi Arabia

Outside of China, almost 80 percent of all executions were recorded in Iran, Iraq and Saudi Arabia. Iran is reported to have executed 369 people, and Iraq is recorded as having executed 169, according to Amnesty.

At least 23,392 people were sentenced to death worldwide by the end of 2013, the rights group said, with most of the sentences related to drugs offences.

The United States remained the only country in the Americas that carries out executions. The state of Texas accounted for 41 percent of them.

According to Amnesty International's annual report, by 2013, 173 of the 193 member states of the United Nations were execution free.