Riyadh (AFP) - The Supreme Court in Saudi Arabia has confirmed the death sentence against Shiite cleric Sheikh Nimr al-Nimr, a leader of anti-government protests, one of his brothers said on Sunday.

"After the confirmation of Sheikh Nimr's death sentence by the Court of Appeal and then the Supreme Court, his life is in the hands of King Salman who can endorse the sentence or suspend the execution," said Mohammed al-Nimr.

He warned his brother's execution "could provoke reactions that we do not want," as Sheikh Nimr had "supporters in the Shiite areas of the Islamic world".

Mohammed al-Nimr said he expected the king to "prove his wisdom" by halting the execution of his brother and six other Shiites.

Among those sentenced to death, "three, including my son Ali, were minors at the time of arrest" for involvement in anti-government protests that erupted in the Eastern Province in the wake of the Arab Spring, he told AFP.

The case of Ali al-Nimr, in particular, has aroused strong reactions around the world, with many asking the Saudi authorities to grant the young Shiite a stay the execution.

Iran, the arch-foe of Saudi Arabia, on Sunday warned Riyadh not to execute the cleric.

"The execution of Sheikh Nimr would have dire consequences for Saudi Arabia," said Deputy Foreign Minister Hossein Amir Abdollahian.

"The situation in Saudi Arabia is not good and provocative and tribal attitudes against its own citizens are not in the government's interests," he said in a statement.

Sheikh Nimr had called in 2009 for separating the Eastern Province's Shiite-populated Qatif and Al-Ihsaa governorates from Saudi Arabia and uniting them with Shiite-majority Bahrain.

Last year a special court in Riyadh sentenced him to death for "sedition", "disobedience" and "bearing arms".

Saudi Arabia's estimated two million Shiites, who frequently complain of marginalisation, live mostly in the east, where the vast majority of the OPEC kingpin's huge oil reserves lie.