The European Union's foreign policy chief warned Iran's foreign minister on Sunday that renewed tension between Shiite Iran and Saudi Arabia's Sunni monarchy could wreck efforts to find a political solution for the crisis in Syria.

Federica Mogherini said in a statement that she had spoken by telephone with Iranian Foreign Minister Javad Zarif at length on Sunday morning after violence erupted in Iran following Saudi Arabia's execution of a Shiite cleric.

Mogherini said she and Zarif had agreed that no effort should be spared by all parties to keep the situation under control and to prevent sectarian tensions from escalating.

"The international community and the main regional actors are actively working together to support a political solution for the crisis in Syria and to join forces against terrorist groups, and these efforts should not be jeopardized by new instability," Mogherini said.

Mogherini said that she had been informed of the storming of the Saudi embassy in Tehran by protesters and of steps taken by the Iranian authorities to defuse tensions and protect the Saudi diplomats.

Mogherini also spoke by phone in the afternoon with Saudi foreign minister Adel al-Jubeir, reiterating the EU's opposition to the death penalty and expressing concern over the risk of an escalation of sectarian violence.