- How do Sunni and Shiite Islam differ?
- Image compares Saudi Arabia with IS
- Analysis: Saudi royals put faith in the sword
- Forecast: Iran and Saudi Arabia tensions to worsen
Tensions between Saudi Arabia and Iran, which began with the kingdom's execution of a Shiite cleric and escalated with attacks on Saudi diplomatic posts in the Islamic Republic, have countries around the world responding by choosing sides or urging calm.
Iraqi violence over Saudi execution
Earthquake devastates central Italy
Earthquake strikes central Italy
North Korea fires missile from submarine
Team Great Britain's baggage collection fail
Fisherman's pearl could be largest ever
Hillary Clinton opens pickle jar
Vigil for deaf man fatally shot
Iraqi violence over Saudi execution
Thousands across Iraq protest the Saudi execution of a prominent Shi'ite cleric and at least two Sunni Muslim mosques are attacked south of Baghdad in an apparent retaliation for the killing.
Some nations have followed the Saudis' lead in severing or downgrading ties with Iran, while others have offered words of caution aimed at calming the situation.
Here's a look at where countries and other regional actors stand at this point:
The main actors:
Saudi Arabia – The kingdom severed ties to Iran after attacks on two of its diplomatic posts following its execution of a Shiite cleric last weekend. It also later cancelled all flights between the two nations.
Iran – Since the attack on the diplomatic posts, Iran says it has made arrests and has criticised the violent protesters. However on Tuesday, President Hassan Rouhani took a slightly harder line, saying Saudi Arabia's move to sever ties with his country couldn't "cover its crime" of executing Shiite cleric Nimr al-Nimr.
Countries backing Saudi Arabia:
Bahrain – The tiny, Shiite-majority island kingdom off the Saudi coast, which long has relied on Riyadh for support of its Sunni rulers, was the first to cut ties with Iran and has also halted flights. Bahraini officials have repeatedly accused Iran of training militants and attempting to smuggle arms into the country, which hosts the US Navy's 5th Fleet.
Sudan – The African nation cut diplomatic ties to Iran and gave Iranian diplomats two weeks to leave the country. Sudan once tilted toward Iran, but has been looking to Saudi Arabia for aid since the secession of oil-rich South Sudan in 2011.
United Arab Emirates – The oil-rich country of seven emirates says it will reduce the number of diplomats in Iran, recall its ambassador and focus only on business relations. While backing Saudi Arabia, it may have chosen to reduce – rather than completely sever ties – because of a long trading history with Iran.
Kuwait – The oil-rich country is recalling of its ambassador from Tehran, but it isn't immediately clear how Kuwaiti-Iranian diplomatic ties will be affected. Tiny Kuwait is home to both Shiites and Sunnis living in peace and has the most free-wheeling political system among all Gulf nations.
Jordan – Overwhelmingly Sunni Jordan is a close ally of Saudi Arabia in the region and a beneficiary of Gulf aid. Jordan's government spokesman, Mohammed Momani, has condemned the attack on the Saudi Embassy in Iran.
Egypt – Visiting Riyadh on Tuesday, Egyptian Foreign Minister Sameh Shoukry denounced the attacks on Saudi diplomatic missions in Iran and said Iran's behaviour after al-Nimr's execution amounts to "intervening in the kingdom's internal affairs." Cairo has been closely allied with Riyadh since the Egyptian military overthrew an Islamist president in 2013. Riyadh has provided billions in aid to Egypt since then.
The Arab League – The body denounced the attacks on the diplomatic missions and reminded Iran of the importance of "not interfering in the internal affairs of an Arab nation," according to a statement carried by Egypt's official MENA news agency.
Oman – The sultanate has long historical ties to Iran and served as the base for secret talks between Iranian and US officials that jump-started the international deal reached on Iran's contested nuclear program.
Those backing Iran:
Lebanese Hezbollah movement – Hezbollah was founded in 1982 with the help of Iran's Revolutionary Guard after Israel invaded Lebanon. The group is one the main Iran-backed factions in the region.
Syrian president Bashar Assad – Iran has been one of the biggest supporters of Syria since the 1980s and has stood by Assad's government in his country's grinding civil war. Saudi Arabia has been one of the biggest backers of those trying to overthrow him.
Iraq's Shiite-led government – Al-Nimr's execution sparked outrage among the country's majority Shiites, who have taken to the streets in Baghdad and the south, calling for an end to ties with Saudi Arabia. The Shiite-led government has warmed Riyadh that such executions "would lead to nothing but more destruction."
Other regional actors:
Israel – Israel considers Iran to be its greatest regional threat because of its nuclear program, its arsenal of long-range missiles, its support of anti-Israel militant groups and its repeated threats to destroy it. While Israel has no direct ties to Saudi Arabia, the countries have a shared concern over Iran's growing influence.
The Palestinians – The Palestinian Authority issued a statement after the execution of al-Nimr saying that it stands alongside the Saudis in their fight against "terrorism." The Saudis are the largest donor to the Palestinian Authority in the Arab world, providing them some $200 million annually. The PA, and the Fatah faction that leads it, has had a strained relationship with Iran because of its support of its rival, Hamas.
Yemen – The Arab world's poorest country is torn by a civil war pitting its internationally recognised government, backed by a Saudi-led coalition, against Shiite rebels known as Houthis, who are supported by Iran.
Those urging caution:
The United Nations – UN Secretary-General Ban Ki-moon has urged Saudi Arabia and Iran to support peace efforts in Syria and Yemen and avoid escalating tensions.
European Union – The 28-nation bloc, which opposes the death penalty, criticised Saudi Arabia's mass executions and said al-Nimr's case undermined freedom of expression and basic political rights in the kingdom. Since tensions flared between Iran and Saudi Arabia, the EU foreign policy chief has had phone contact with both sides, fearing an escalation would further destabilise the whole region.
The United States – The White House has urged Saudi Arabia and Iran to not let their dispute derail efforts to end the Syrian civil war. President Barack Obama's administration also hopes to see the Iranian nuclear deal through.
United Kingdom – Britain and Iran reopened their respective embassies in 2015, four years after hard-line protesters stormed the British embassy in Tehran. Saudi Arabia is a key diplomatic and economic ally of Britain, though Middle East Minister Tobias Ellwood said Britain told the kingdom about its "disappointment at the mass executions."
Turkey – Turkey has urged both Saudi Arabia and Iran to ease tensions, saying the Middle East region is "already like a powder keg" and cannot withstand a new crisis.
Germany – Berlin has called on Saudi Arabia and Iran to work to mend their diplomatic ties, while condemning both the mass executions in the kingdom and the storming of the Saudi missions in Iran.
Russia – State news agency RIA Novosti quoted an unnamed senior diplomat as saying Moscow is ready to act as a mediator between Iran and Saudi Arabia. It's unclear whether Russian officials have made a formal offer to work with the two nations.