Kerry calls Iranian, Saudi FM to urge calm

US Secretary of State John Kerry has made repeated calls to both Iranian and Saudi leaders to try to defuse the crisis (AFP Photo/Yuri Gripas) (AFP)

Washington (AFP) - US Secretary of State John Kerry called the Iranian and Saudi Arabian foreign ministers on Monday to urge calm after the dramatic breakdown of relations between Tehran and Riyadh.

Speaking on condition of anonymity, US officials said he reached out to his counterparts Mohammad Javad Zarif and Adel Al-Jubeir as the crisis triggered by the Saudi execution of a Shiite cleric deepens.

"We are urging calm and de-escalation. The situation needs to be calmed," one official told AFP.

The United States itself has no formal diplomatic relations with Iran, but has been developing a closer working relationship since signing a deal to limit Tehran's nuclear ambitions in July last year.

Washington is keen to avoid an escalation in tensions with Iran as it works to oversee implementation of that deal and also as it encourages Tehran to play a role in peace talks to end the Syria civil war.

The United States is traditionally a much closer partner to Saudi Arabia, but was angered last week when Riyadh chose to begin 2016 with a mass execution of prisoners, including a respected Shiite cleric accused of inciting protests.

Following Sheikh Nimr al-Nimr's death, Shiite protesters overran the Saudi embassy in Tehran.

Accusing Tehran of allowing the protesters to firebomb its mission, Saudi Arabia and some of its Sunni allies in the region broke off diplomatic ties and flights, threatening to further poison relations.

Saudi Arabia has regularly accused Tehran of sponsoring terror attacks on its soil and of supporting Shiite Huthi rebels fighting the Saudi-backed government in Yemen.

Saudi Arabia and Iran also back opposing sides in the Syrian civil war, with Tehran and its Lebanese militia ally Hezbollah backing President Bashar al-Assad and Riyadh sponsoring various Sunni rebel groups.