Pressure is building over the case of Raif Badawi, the jailed Saudi blogger who is due to be flogged for a second time on Friday as part of his controversial punishment for setting up a website to promote free speech.

The 31-year-old was flogged 50 times in a public square in the port city of Jeddah last week. He was sentenced last May to 10 years in prison, a fine and 1,000 lashes after criticising Saudi Arabia’s powerful clerics on his blog.

The UN high commissioner for human rights, Zeid Raad al-Hussein, said in a statement on Thursday that flogging is “at the very least, a form of cruel and inhuman punishment” prohibited under international human rights law.

Al-Hussein, a member of the Jordanian royal family, appealed to King Abdullah bin Abdelaziz to halt the flogging by pardoning Badawi “and to urgently review this type of extraordinarily harsh penalty.”

Britain has also promised again to raise the case with the Saudi authorities though the Foreign Office refused to say whether representations would be made in person by the UK ambassador in Riyadh, Sir John Jenkins, or whether the Saudi ambassador to London, Prince Mohammed bin Nawwaf bin Abdelaziz, would be summoned to explain his country’s position.

Amnesty International, which has adopted Badawi as a prisoner of conscience, has accused the British government of “wearing the Saudi muzzle” because of its oil, business and strategic interests in the conservative kingdom.

Vigils were held outside Saudi embassies in Berlin, Paris, the Hague and Tunis on Thursday. In Canada, where Badawi’s wife and children now live, the government expressed concern at a punishment it described as “a violation of human dignity and freedom of expression.”

Protesters holding photos of the activist with “#FreeRaif” slogans lined the street outside the Saudi embassy in London.

Ensaf Haidar, Badawi’s wife, told the BBC’s Newshour programme of her anguish when she was told that her husband had been flogged for the first time. “What I felt was indescribable. It was an indescribable mixture of sadness and pain,” she said. “It was painfully horrible to imagine what was happening to Raif.”

Saudis contacted by the Guardian say privately that Badawi is being punished in order to appease a clerical establishment angered by a recent crackdown on jihadis because of the new fear of the Islamic State (Isis) in Syria and Iraq.

Other more radical dissidents who have challenged the monarchy and not just the role of Islam in the kingdom are serving long prison sentences.

The Foreign Office said it was “seriously concerned” at the flogging. “The UK condemns the use of cruel, inhuman or degrading punishment in all circumstances,” a spokesman said. “We have previously raised Mr Badawi’s case and will do so again directly with the Saudi authorities. The UK is a strong supporter of freedom of expression around the world. We believe that people must be allowed to freely discuss and debate issues, challenge their governments, exercise the right to freedom of thought, conscience and religion, and speak out against violations of human rights wherever they occur.”

But expressions of concern have not led to any diplomatic action against Saudi Arabia, which is also regularly criticised for its prodigious use of the death penalty.

The EU’s diplomatic service has also condemned the punishment. It said: “Corporal punishment is unacceptable and contrary to human dignity. As we recently commemorated the 30th anniversary of the adoption of the UN convention against torture and other cruel, inhuman and degrading treatments or punishments, the EU reiterates its strong objection to any such treatment or punishment.

“The process of judicial reform undertaken by the Kingdom of Saudi Arabia opens the possibility for improved protection of individual rights. In this context the EU calls on the Saudi authorities to suspend any further corporal punishment for Mr Badawi and to consider, in the context of the reform, putting an end to the use of lashing, a punishment that is not in conformity with the relevant international conventions on human rights, including the convention against torture, which Saudi Arabia has ratified.”