Activists have once again gathered outside the Saudi embassy in London calling on Riyadh�to halt the execution of�prominent�Shia cleric�Sheikh Nimr Baqi al-Nimr�and his nephew.

The participants in the Wednesday rally held�placards reading �free Sheikh Nimr" and "sentenced to death due to the idea of election system."

"We call on Saudi Arabia to halt these executions and either release these innocent prisoners or we call for...�a fair and public trial under the watchful eyes of the world," Russia's Ruptly�news agency quoted�an activist as saying.

"And we will not be silenced as you do to your citizens in Saudi Arabia,� another activist�said.

On Sunday,�Saudi Arabia�s Supreme Court upheld a death sentence issued against the cleric last year.�The execution warrant will be sent to Saudi King Salman bin Abdulaziz Al Saud to be approved and then implemented.

Sheikh Nimr was attacked and arrested in Saudi Arabia's eastern region of Qatif�in July 2012, and has been charged with undermining the kingdom�s security, making anti-government speeches, and defending political prisoners. He has denied�the accusations.

Ali Mohammed Baqir al-Nimr, the cleric�s nephew, has also been sentenced to death over his alleged role in anti-regime protests in 2012, when he was 17 years old.

"When he joined the protest three years ago he was only 17, he was underage and he only participated in a peaceful protest, you cannot take a boy and... condemn him to death because he protested against you and he called for some political reforms, this is outrageous, this is outside any human decency," said political activist Saeed Shehabi during the protest rally.

Meanwhile, UN Secretary General Ban Ki-Moon has called on Saudi Arabia to halt Nimr�s execution.

Speaking at the UN headquarters in New York, Ban�s spokesmen, Stephane Dujarric, said that during a phone call the UN chief�had asked King Salman�to overturn the death sentence against�the Shia cleric.

By Press TV