RIYADH (Reuters) - Immediately after his sword falls, the Saudi Arabian executioner steps backwards to avoid soiling his clothes with the blood of the condemned man, whose headless body can be seen slumping over backwards in the shaky online film.

After perfunctorily checking the white folds of his robe for flecks of red, the executioner wipes his blade with a tissue, which he drops onto the corpse and walks away.

A sudden surge in public executions in Saudi Arabia in the last two months has coincided with a U.S.-led bombing campaign against Islamic State. This has led to inevitable comparisons in Western media between Islamic State's beheadings and those practiced in Saudi Arabia.

Defenders of the Saudi death penalty say beheadings, usually with a single sword stroke, are at least as humane as lethal injections in the United States. They deplore any comparison between the kingdom's execution of convicted criminals and Islamic State's extra-judicial killing of innocent hostages.

But rights activists say they are more concerned by the justice system behind the death penalty in the kingdom than by its particular method of execution. And critics of the Al Saud ruling family say the latest wave of executions may have a political message, with Riyadh determined to demonstrate its toughness at a moment of regional turmoil.

Saudi Arabia beheaded 26 people in August, more than in the first seven months of the year combined. The total for the year now stands at 59, compared to 69 for all of last year, according to Human Rights Watch.

"It's possible the executions were used as intimidation and flexing of muscles. It's a very volatile time and executions do serve a purpose when they're done en masse," said Madawi al-Rasheed, visiting professor at the Middle East Centre of the London School of Economics.

"There's uncertainty around Saudi Arabia from the north and from the south and inside they are taking aggressive action alongside the U.S. against Islamic State, and all that is creating some kind of upheaval, which the death penalty tries to keep a lid on."

A spokesman for Saudi Arabia's Justice Ministry was not immediately available to explain the upsurge in executions in August, or to answer other questions about the kingdom's use of the death penalty.

"PARTICULARLY EGREGIOUS"

Whatever the reason for the timing, the wave of executions at the same time as jihadis in Iraq and Syria were beheading captives has brought new scrutiny to the practices of a country whose values are so different from those of its Western allies.

While Saudi Arabia has joined U.S.-led air strikes against Islamic State in Syria and has deployed its senior clergy to denounce militant ideology, its public beheading of convicts, particularly for non-violent or victimless crimes like adultery, apostasy and witchcraft, is anathema to Western allies.

"Any execution is appalling, but executions for crimes such as drug smuggling or sorcery that result in no loss of life are particularly egregious," said Sarah Leah Whitson, Middle East and North Africa director for Human Rights Watch.

Some diplomats have said the increase may be only a quirk of timing, as the appointment of more judges has allowed courts to clear a backlog of appeal cases, and as the rise began after the end of Ramadan, when fewer executions traditionally occur.

But the interpretation of it as a show of strength appeared to be reinforced last week by the sentencing to death of Sheikh Nimr al-Nimr, a member of the Sunni-ruled kingdom's Shi'ite minority who had backed protests in 2011.

Two other men, one of whom was younger than 18 at the time of the protests, have also been sentenced for their part in the demonstrations and were convicted of having thrown petrol bombs.

"If you look at the definition of what Nimr was sentenced for, instigating sedition, it shows they want to make sure they stop any form of activism," said Mai Yamani, a Saudi-born political analyst in London.

More than a dozen people convicted of terrorism or Sunni Islamist militancy have also been sentenced to death this year.

BLACK MAGIC, ADULTERY AND APOSTASY

Under the Saudi Sharia legal system it can actually be harder to avert execution for crimes without a specific victim, like drug smuggling, than for murder.

Of the 59 people executed by Oct. 16, 22 had been convicted for smuggling drugs, according to figures compiled by Human Rights Watch from Saudi media reports.

One Saudi man, Mohammed Bakr al-Alaawi, was put to death for sorcery so far this year, the third such case since 2011. Although such cases are even rarer, judges can also demand execution for adulterers or Muslims who abandon their faith.

In Saudi Islamic law, charges of violent crimes like murder are usually brought under the system of "qisas": retaliation on the principle of an eye for an eye.

While a murderer would normally be sentenced to death, the victim's family is permitted to accept "diyya", or blood money, instead of execution. The lives of women are worth half those of men, and non-Muslims a fraction of the value of Muslims.

Convicts from less wealthy backgrounds, or without tribal connections who might intercede with the family or tribe of the victim, are more likely to die because it is harder for them to arrange a blood money payment.

For other crimes, the punishment is usually up to the judge, employing his own interpretation of ancient Muslim texts. When there is no victim, there is no victim's family to offer mercy at a price. Saudi Arabia has no civil penal code that sets out sentencing rules, and no system of judicial precedent that would make the outcome of cases predictable based on past practice.

Bassim Alim, who defended 17 men who were sentenced to up to 30 years jail in 2011 for sedition and other crimes in a high profile political case, said judges saw no need for many protections seen as fundamental in the west, like ensuring defendants had legal representation.

"The judge actually told one of the accused to my face: 'Why do you need a lawyer? You don't need a lawyer'," he said.

Alim said capital convictions were often based on no evidence other than a confession, with judges under no obligation to consider mitigating circumstances, psychological factors or the possibility that a confession was coerced.

REFORM STALLED

King Abdullah announced plans for legal reform in 2007, but judges, drawn from the traditionally conservative clergy, have so far succeeded is putting off meaningful change.

In 2009 Abdullah replaced the long-serving, conservative justice minister with a younger scholar, Mohammed al-Issa. His attempts to introduce more modern training for judges and a system of precedent to make sentencing more predictable have so far been blocked by strenuous opposition from conservatives.

Even Saudis who want reform generally do not oppose the use of the death penalty by public beheading. Khalid al-Dakheel, a political sociology professor in Riyadh, said the turbulence in the region meant people wanted the justice system to be tough.

"You don't want to have a dictatorship similar to that of Bashar al-Assad in Syria or (former Iraqi leader) Saddam Hussein. But at the same time you don't want to have a government which is weak, especially in such a region and at such a time," he said.

In the most extreme version of the Saudi death penalty, known by the Arabic word for "crucifixion" and reserved for crimes that outrage Saudi society, the corpse is publicly hanged in a harness from a metal gibbet as a warning to others.

An online film dated April 2012 on the LiveLeaks website shows a man being executed and then "crucified" in this manner, reportedly for robbing a house and killing its occupants. A group of five men suffered this fate in May last year in the southern province of Jizan for a series of robberies.

The reformist Jeddah lawyer, Alim, said he supported capital punishment in Saudi Arabia but that the legal system needed to be strengthened to ensure verdicts were just.

"I'm not someone who shies away from it. It's part of Sharia. But it has to be handled with extreme sensitivity and care. At the moment it can be done on the basis of no other evidence if the accused confesses," he said.

(Reporting by Angus McDowall; Editing by Peter Graff)