Saudi Arabia has executed at least 151 people this year — the most since 1995 and far above the annual figure in recent years, which rarely exceeded 90, Amnesty International said on Monday.

No one at Saudi Arabia's Justice Ministry was immediately available to comment on the surge in executions, but diplomats have speculated that it may be because more judges have been appointed, allowing a backlog of appeals to be heard.

Political analysts say it might also reflect a tough response to wars and political turbulence in the region.

By June of this year, the country surpassed its number of executions for all of 2014.

Among those on the country's death row is Ali al-Nimr, who is to be put to death by crucifixion. Arrested at 17 for participating in an illegal demonstration, Nimr has drawn international attention for his case.

Abdallah al-Mouallimi, Saudi Arabia's permanent U.N. representative, told Al Jazeera America in October that no date had yet been set for Nimr's execution.

Another activist, Dawoud al-Marhoon, also 17 at the time of his arrest, has been sentenced to death by beheading.

The kingdom was ranked third for number of executions in 2014, after China and Iran and ahead of Iraq and the United States, according to Amnesty International figures. Those five countries executed the most prisoners in the first six months of 2015, Amnesty said in July.

The last time Saudi Arabia executed more than 150 people in a year was in 1995, when 192 executions were recorded, Amnesty International said in a statement.

Defenders of the Saudi death penalty say beheadings, usually with a single sword stroke, are at least as humane as lethal injections used in the United States. They deplore any comparison between its executions of convicted criminals and extrajudicial killings of hostages by the Islamic State in Iraq and the Levant.

Amnesty International said the death penalty is disproportionately used against foreigners in Saudi Arabia. Of the 63 people executed this year for drug-related charges, 45 were foreigners. So far this year, 71 foreigners have been executed in the country.

Mostly guest workers from poor countries, foreigners in Saudi Arabia are particularly vulnerable because they typically do not know Arabic and are denied adequate interpretation services in court, Amnesty said.

Saudi Arabia says it provides fair trials for all defendants.

Al Jazeera and wire services