The number of known executions worldwide rose to at least 778 in 2013 - a 15 percent rise from the year before- following a surge in Iraq and Iran, Amnesty International said.

China remains the world's biggest state executioner by far, the London-based human rights organisation said in a report released on Thursday. Beijing is thought to have killed thousands of its own citizens, more than the rest of the world put together, it said.

The organisation’s annual report on death sentences and executions worldwide said the Chinese authorities "continue to treat the figures on death sentences and executions as a state secret".

Those states who cling to the death penalty are on the wrong side of history and are, in fact, growing more and more isolated.

Salil Shetty, Amnesty International's secretary-general

Although Beijing said in November it would reduce the number of crimes eligible for the death penalty from the current 55, it still led the top five countries using the death penalty in 2013, followed by Iran, Iraq, Saudi Arabia and the United States.

The rise in the known judicial uses of the death penalty - from at least 682 in 2012 - was chiefly due to Iraq and Iran, the report said.

Iraq executed at least 169 people in 2013, a sharp rise on the 40 given the death penalty in 2011 and 101 put to death in 2010, with death sentences there often passed after "grossly unfair trials", the report said.

Iran put at least 369 people to death in 2013, up from at least 314 in 2012, and Amnesty said there was credible evidence from sources in the country that at least 335 further executions were carried out in secret.

"The virtual killing sprees we saw in countries like Iran and Iraq were shameful," said Salil Shetty, Amnesty International's secretary-general.

"But those states who cling to the death penalty are on the wrong side of history and are, in fact, growing more and more isolated."

China defended its use of the death penalty as traditional deterrent.

"The relevant organisation always has biased opinions against China," Foreign Ministry spokesman Hong Lei said.

At least 79 people were put to death in Saudi Arabia, including at least three people suspected to be minors.

The US, is the only country in the Americas that carried out executions in 2013, with 39 people killed.

Source: Agencies