Saudi Arabia will pay "a high price" for executing prominent Shia cleric Nimr al-Nimr on Saturday, Iran's foreign ministry said.
Ministry spokesman Hossein Jaber Ansari strongly condemned the execution, which came after his Shia country repeatedly asked its Sunni-ruled rival to pardon the cleric.
"The Saudi government supports terrorist movements and extremists, but confronts domestic critics with oppression and execution... the Saudi government will pay a high price for following these policies," he said, quoted by the official IRNA news agency.
Nimr, 56, was a driving force of the protests that broke out in 2011 in Eastern Province, where the Shia minority of Saudi Arabia complains of marginalisation.
"The execution of a figure like Sheikh al-Nimr, who had no means to follow his political and religious goals but through speaking out, merely shows the extent of irresponsibility and imprudence," said Ansari.
For its part, the Basij student militia connected to Iran's elite Revolutionary Guards called for a demonstration on Sunday afternoon in front of the Saudi embassy in Tehran.