Bahrain and Sudan have joined Saudi Arabia in cutting ties with Iran in the wake of the execution of a prominent Shiite cleric.

Key points: Bahrain and Sudan join Saudi Arabia in cutting ties with Iran

Bahrain and Sudan join Saudi Arabia in cutting ties with Iran Decision triggered by attack on Saudi diplomatic mission in Tehran

Decision triggered by attack on Saudi diplomatic mission in Tehran Russia says it is ready to act as 'intermediary' between Iran and Saudi Arabia

Russia says it is ready to act as 'intermediary' between Iran and Saudi Arabia Two Sunni mosques attacked in Iraq

The decision from Bahrain was triggered by "cowardly" attacks on the Saudi diplomatic mission in Iran and "increasing flagrant and dangerous meddling" by Tehran in the internal affairs of Gulf and Arab states, a statement said.

Sudan's foreign ministry later released a statement saying: "In response to the barbaric attacks on the Saudi Arabian Embassy in Tehran and its consulate in Mashhad ... the government of Sudan announces the immediate severing of ties with the Islamic Republic of Iran."

Saudi Arabia cut ties with Iran after Iranian protesters attacked its mission there, angered by the Sunni Muslim kingdom's decision to execute Sheikh Nimr al-Nimr, a leading Shiite cleric.

Iranian diplomats in Saudi Arabia and Bahrain have been given a 48-hour deadline to leave.

Saudi Arabia later widened its rift with Iran, saying it would end all air traffic and trade with Iran, according to Foreign Minister Adel al-Jubeir.

Insisting Riyadh would react to "Iranian aggression", Mr Jubeir accused Tehran of despatching fighters to Arab countries and plotting attacks inside the kingdom and its Gulf neighbours.

The United Arab Emirates — an ally of both Saudi Arabia and Bahrain — has said it would downgrade its diplomatic representation in Iran and limit the number of Iranian diplomats in the country, state news agency WAM reported.

Sheikh Nimr was beheaded on the weekend after Saudi authorities accused him of inciting his followers to violence, but he was hailed in Iran as a champion of the rights of Saudi Arabia's marginalised Shiite minority.

Bahrain, like Saudi Arabia, has a Sunni royal family, while Iran is the main Shiite power.

Analysts have speculated that the execution of Sheikh Nimr and the other Shiites was partly to demonstrate to Saudi Arabia's majority Sunni Muslims that the government did not differentiate between political violence committed by members of the two sects.

Russia, West urges dialogue, de-escalation

Bahrain's move came after Russia said it was ready to act as an intermediary to help settle tensions between Iran and Saudi Arabia.

A Russian Foreign Ministry source, speaking on condition of anonymity, told Russian news agencies Moscow would be prepared to play the peacemaker.

"As friends we would be ready to play, if it is demanded, an intermediary role in ... settling the existing contradictions and any new ones that arise between these two countries," RIA cited the source as saying.

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The United States urged leaders in the Middle East to take measures to soothe tensions.

"We're aware that the Kingdom of Saudi Arabia has ordered the closure of Iranian diplomatic missions in the kingdom," US State Department spokesman John Kirby said.

"We believe that diplomatic engagement and direct conversations remain essential in working through differences and we will continue to urge leaders across the region to take affirmative steps to calm tensions."

UN Secretary-General Ban Ki-moon told the Saudi foreign minister Riyadh's decision to break off diplomatic ties with Iran was extremely troubling, a spokesman for the United Nations said.

"The Secretary-General reiterated that the attack on the Saudi embassy in Tehran was deplorable, but added that the announcement of a break in Saudi diplomatic relations with Tehran was deeply worrying," UN spokesman Stephane Dujarric said.

Germany called on Saudi Arabia and Iran to use all options to resolve the conflict.

"We urge both countries to engage in dialogue," German government spokesman Steffen Seibert told a news conference.

Shiite protests, Sunni mosques attacked killing 'prayer caller'

Demonstrators took to the streets of Tehran for a third consecutive day of protests on Monday after the Saudi Arabia execution of Shiite Sheikh Nimr.

Some 3,000 demonstrators gathered in Imam Hossein Square in eastern Tehran, chanting slogans against Saudi Arabia's Al-Saud royal family.

In Iraq, a Shiite-majority country, thousands of protesters also marched in Baghdad and Iraq's southern Shiite cities on Monday condemning the execution.

In Baghdad, demonstrators carrying portraits of Nimr rallied outside the Green Zone, a heavily fortified district that houses government departments and diplomatic representations, including the newly reopened Saudi embassy.

Iraqi men protest against the execution of Shiite Muslim cleric Nimr al-Nimr in Saudi Arabia. ( Reuters: Alaa al-marjani )

Police guarding the zone pushed back a group that attempted to cross a line of barbed wire as they chanted "Damned, damned be Al Saud!," referring to the Saudi ruling family.

Similar protests were held in Basra, southern Iraq's biggest city, and in the holy Shiite cities of Najaf and Kerbala.

"Killing Sheikh Nimr is the beginning of your downfall," shouted demonstrators in Kerbala, addressing the Saudi ruling family.

They carried a coffin symbolising a funeral for the cleric.

On Sunday night (local time), at least two Sunni mosques were reported to have been attacked in Baghdad in apparent retaliation for Sheikh Nimr's execution.

The interior ministry in Baghdad confirmed the attacks late Sunday night in Hilla, about 100 kilometres south of Baghdad.

A muezzin — the person appointed to recite the Muslim call to prayer — was gunned down and killed in the overnight attacks in the same region.

A Hilla doctor confirmed the death.

Iraq has faced sectarian bloodletting for years, mainly between the Sunni minority and Shiite majority that was empowered after the US-led invasion in 2003.

Prime Minister Haider al-Abadi ordered the provincial authorities "to chase the criminal gangs" who attacked the mosques.

He blamed the attacks on "Daesh and those who are similar to them," according to a statement that refers to Islamic State by one of its Arabic acronyms.

The attack on the Ammar bin Yasir mosque in the northern outskirts of Hilla destroyed its dome and several walls, according to a Reuters cameraman who visited the site.

The second attack on the al-Fath al-Mubeen mosque in central Hilla was reported by a provincial council member and a police source who said a guard inside the building was killed.

Earlier, gunmen firing at Saudi Arabian police in Sheikh Nimr's home village killed a civilian and wounded a child, according to Saudi Arabia's official SPA news agency.

AFP/Reuters