Saudi Arabia’s King Salman bin Abdul-Aziz Al Saud has already overseen his first beheading just days after succeeding his brother, ignoring widespread claims that the case against the man was weak.

The controversial killing of Moussa al-Zahrani came shortly before President Barack Obama arrived in Riyadh on Tuesday to pay respects to the late King Abdullah.

Al-Zahrani, a teacher, was executed in the city of Jeddah. He had been convicted of sexually assaulting underage girls in a string of attacks in 2011. Al-Zahrani had maintained his innocence throughout two appeals and released a 20-minute video urging King Abdullah to intervene last year.

His case drew an unprecedented reaction from those living in Saudi Arabia on social media but King Salman, 79, refused to intervene and he was beheaded on Monday.

An Arabic hashtag on Twitter, "We are all Moussa al-Zahrani", garnered thousands of comments by Saudis, with conflicting opinions over the case.

Al-Zahrani's relatives had gone on Saudi talk shows and claimed the case against him was riddled with inconsitancies. They said several cases of assault against young girls took place while al-Zahrani was already jailed.

Amnesty International condemned news that an execution had already taken place.

Sevag Kechichian, Amnesty's Saudi Arabia researcher, told The Independent: "It's extremely distressing to see that the Saudi executioner has already been at work, just days after King Salman bin Abdulaziz Al Saud ascended the throne.

"The Saudi Arabian authorities should establish an immediate moratorium on executions with a view towards abolishing the use of the death penalty once and for all."

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Al-Zahrani's brother, Hassan al-Zahrani, said after the execution that his brother, a father of six, could not have committed the crimes he was convicted of.

His death comes after the state publicly beheaded a woman in the holy city of Mecca last week for murdering her seven-year-old daughter. A gruesome video of her death marked the tenth execution in 2015, while 87 people were executed the year previous.

Kind Salman was governor of Riyadah for 48 years and had already taken on many duties as his brother’s health declined.

The King is believed to be less interested in social reform as King Abdullah was, who engendered a very moderate series of reforms during his reign.

President Obama addressed the Kingdom’s poor human rights record before embarking on his visit. He acknowledged that the US willingness to pursue close ties with Saudi Arabia despite human rights abuses often makes America's allies uncomfortable.

"Sometimes we need to balance our need to speak to them about human rights issues with immediate concerns we have in terms of counterterrorism or dealing with regional stability," he told CNN.