The number of death sentences handed down in the US, 32, was the lowest since 1973 and the number of executions, 20, meant the country is now no longer among the world's five biggest executioners

US death penalty sentences fell to a historic low last year and executions also dropped sharply, contributing to a global slump of over a third from 2015, Amnesty International said Tuesday.

The number of death sentences handed down in the US, 32, was the lowest since 1973 and the number of executions, 20, meant the country is now no longer among the world's five biggest executioners.

Salil Shetty, secretary general of the London-based international human rights watchdog, said the US decline was "a sign of hope for activists who have long campaigned for an end to capital punishment".

"The debate is clearly shifting," he said in the group's annual global review of the death penalty, which showed a 37 percent decline overall.

Amnesty said it was "a clear sign that judges, prosecutors and juries are turning their back on the death penalty as a means of administering justice".

The report also noted sharp drops in the number of executions in Iran -- down 42 percent to at least 567 -- and Pakistan -- down 73 percent to 87.

There were also fewer executions in sub-Saharan Africa, although the number of death sentences handed down more than doubled to 1,086, largely due to a rise in Nigeria to 527 from 171.

- China 'leading' in executions -

Overall Amnesty recorded 1,032 executions worldwide last year -- a 37-percent decline from 2015.

In 2015, Amnesty said worldwide executions had reached 1,634 -- the highest recorded since 1989.

The statistics exclude China which Amnesty said executes more people than the rest of the world combined but keeps the precise numbers secret.

"China wants to be a leader on the world stage, but when it comes to the death penalty it is leading in the worst possible way -- executing more people annually than any other country in the world.

"It is high time for China to lift the veil on this deadly secret and finally come clean about its death penalty system," Shetty said.

Amnesty found public news reports of at least 931 people executed between 2014 and 2016, which it said was a fraction of the total executions believed to have taken place in China. But it said only 85 of the executions were registered in a state database.

The five biggest executioners in 2016 were China, Iran, Saudi Arabia, Iraq and Pakistan.

Egypt came in sixth place with a doubling of executions to 44 in 2016 from 22 in 2015.

"Under (President) Abdel Fattah al-Sisi's rule Egypt has witnessed an unprecedented increase in mass death sentences after unfair trials," Amnesty said.

Egyptian President Abdel Fattah al-Sisi announced a three-month state of emergency following twin church bombings by the Islamic State group that killed dozens of people on Palm Sunday, the deadliest attacks on the minority in recent memory.