They have never been the best of friends, and a recent escalation in tensions means Saudi Arabia and Iran are unlikely to become allies anytime soon.

A Yemeni missile attack, the resignation of Lebanon's prime minister and a crown prince moving to consolidate his power have all seen tensions flare up across the region once again.

While experts agree the risk of military conflict remains low, there is no doubt the "Cold War" between Middle East rivals has been heating up for months.

The recent flare ups are just the start of a long list of incidents between the two powerhouses whose longstanding rivalry predates the Iranian revolution of 1979.

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It also predates the advent of the Islamic Republic which was a key financial backer of Iraqi dictator Saddam Hussein during his 1980-1988 war with Iran.

Tensions flare

The tensions have been months in the making.

Riyadh and Tehran broke off diplomatic relations in January 2016 after Iranians stormed Saudi Arabia's embassy and consulate in response to the execution of a prominent Shiite cleric.

That followed the 2015 nuclear deal between Tehran and six world powers, which Riyadh feared was a step towards ending Iran's international isolation.

Rhetoric between the two powers grew increasingly belligerent, including over Saudi Arabia's Gulf neighbour Qatar.

Riyadh and several of its Sunni allies broke off diplomatic relations with Qatar in June 2017, accusing Doha of support for extremism and links with Iran, claims that it denies.

This month the animosity reached new heights.

People gather at the site of a Saudi-led airstrike near Yemen's Defense Ministry complex in Sanaa, Yemen. Photo / AP
People gather at the site of a Saudi-led airstrike near Yemen's Defense Ministry complex in Sanaa, Yemen. Photo / AP

First, the Saudi-supported prime minister of Lebanon, Saad al-Hariri, in a broadcast from Riyadh announced his resignation, blaming Iran's "grip" on his country via Shiite movement Hezbollah.

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Several hours later, Saudi Arabia said its air defences near Riyadh intercepted and destroyed a missile fired from Yemen, where a Saudi-led coalition is battling Iran-backed Shiite rebels.

That set off a fierce war of words between Riyadh and Tehran, with Saudi Arabia's powerful Crown Prince Mohammed bin Salman accusing Iran of "direct military aggression".

Tehran denied any involvement in the missile attack, with President Hassan Rouhani warning that Iranian "might" would fend off any challenge.

Why now?

Pointing to wars in Iraq, Syria and Yemen, Clement Therme, a researcher at the International Institute for Strategic Studies (IISS) told the AFP the main cause of the current tensions is related to the "proxy confrontation between Iran and Saudi Arabia".

Recent months have seen changes in these confrontations that appear to have brought the tensions to a head, he said.

In Iraq and Syria, the increasingly successful campaign against the Islamic State group has changed the situation on the ground. Offensives in both countries have forced the jihadists from nearly all the territory they seized in mid-2014.

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Lebanon's Prime Minister Saad Hariri gives a live TV interview in Riyadh insisting he will return to his country within days. Photo / AP
Lebanon's Prime Minister Saad Hariri gives a live TV interview in Riyadh insisting he will return to his country within days. Photo / AP

As Iraq looks to a post-IS era, Riyadh has been taking steps to build stronger ties with the country's Shiite-dominated government.

A flurry of visits between the two countries this year saw talk of a warming of ties, including a trip by Prime Minister Haider al-Abadi to Riyadh in late October.

In Syria, meanwhile, the Iran-backed government of President Bashar al-Assad has over the past year managed to reassert control over large parts of the country by defeating, among others, rebel groups backed by Riyadh.

Growing ambition

Lowy Institute research fellow Dr Rodger Shanahan, an expert on Middle East security, told news.com.au it was important to take a deep breath when using the term "Cold War".

Dr Shanahan said there had been significant tension between the two Middle Eastern nations for years but that had increased recently with several events, including the rise of Saudi Arabia's powerful Crown Prince Mohammed bin Salman.

He said the crown prince was trying to show he's "investing in the Kingdom for generations to come" by appealing to core Saudi youth with social policies such as allowing women to drive and by consolidating his power.

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"At the same time arrests of intellectuals and clerics has sent a strong message to the clerical class that there's a new king who's going to be around for a long time," he said.

His anti-corruption crackdown on elite and powerful businessmen was also designed to show potential opponents who was in charge and he was in control of state intelligence.

Dr Shanahan said the crown prince was also showing the elite he was in charge and that he was an ally not to be criticised.

Almost 50 Saudi royals and dignitaries arrested by the Crown Prince's anti corruption committee in a tough crackdown last week.

Military officials and government ministers as well as 11 princes - among them Prince Alwaleed bin Talal - the 10th richest man on the planet - were among those arrested.

The crown prince is looking to "solidify his position" as he pursues an anti-corruption purge some see as an attempt to cement his hold on power, Dr Shanahan said.

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"Saudi is trying to regain the regional influence it has had in the past," Dr Shanahan said.

"With ISIS defeated Saudi is showing its influential in Iraq and Syria."

Saudi King Salman presents President Donald Trump with The Collar of Abdulaziz Al Saud Medal at the Royal Court Palace. Photo / AP
Saudi King Salman presents President Donald Trump with The Collar of Abdulaziz Al Saud Medal at the Royal Court Palace. Photo / AP

The Trump effect

Domestic and regional influences are not only at play.

Analysts said the election of US president Donald Trump a year ago has also contributed to the rise in recent tensions.

Trump's open hostility towards Tehran has emboldened Riyadh, according to Dr Ben Rich, a lecturer in International Relations at the Department of Social Sciences and Security Studies at Curtin University.

"It's certainly been an intense couple of weeks," Dr Rich said.

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"Saudi and Iran rivalry dates back before the 1979 (Iran) revolution, they are two natural hegemons in the region."

Dr Rich pointed out the Trump administration's support for Saudi Arabia was in contrast to the Obama administration which tried to bring Iran in from the cold by turning a blind eye and offering the country an olive branch.

"The Trump administration has pulled a 180 on that and this has emboldened Saudi," he said.

Dr Rich said the Crown Prince was appealing on a domestic and international level by trying to break away from some traditional norms.

"The crown prince is showing he's more willing to be proactive and confrontational," he said.

The two Middle Eastern nations have traditionally been on different sides when it comes to Iraq, Syria and also Qatar.

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Dr Rich said King Salman had given his son significant power and sees him as the heir to the throne however despite announcing significant reforms has yet to actually implement any significant ones so far.

Soaring tensions with Iran help legitimise his hold on power for someone relatively young.

Leader quits

As tensions rise, Lebanese Prime Minister Saad al-Hariri said he will return to Lebanon from Saudi Arabia in two or three days to affirm that he has quit.

In an interview with a television station that he owns, the Saudi-allied Hariri, Lebanon's most influential Sunni Muslim politician, Mr al-Hariri gave his first public comments since he read out his resignation on television from Riyadh eight days ago.

He said Lebanon was at risk of Arab economic sanctions because of what he described as interventions in Yemen and Bahrain by the powerful, Iran-backed Lebanese group Hezbollah, which is part of the coalition government Hariri has led, Reuters reported.

Mr al-Hariri, who has not returned to Lebanon since he declared his shock resignation, said he stepped down for the sake of the Lebanese national interest, repeatedly saying the country must stick by a policy of "disassociation" from regional conflict.

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After announcing his resignation, Saudi Arabia accused Lebanon of declaring war against it because of Hezbollah.

Writing in Defense One, Robert Malley, vice president for policy at the International Crisis Group, said Lebanon has always been used as a venue for proxy wars between the region's powerful actors.

According to him the Crown Prince wanted the Lebanese Prime Minister to step down and he is determined to depict Tehran as the source of all regional evils.

"For Hariri to preside over a government that includes Hezbollah fundamentally undercut that core message: It meant allowing one of Riyadh's closest allies to co-operate with Tehran's most loyal partner," he writes.

"Hariri as prime minister created the impression that coexistence with Hezbollah and by extension with Iran was possible; his departure is designed to erase any doubt."