Israel struck Iran on Friday morning in an attack that dramatically raises the stakes in a simmering conflict.

Benjamin Netanyahu appears to have defied Western calls for restraint, sparking fears of another major escalation.

As Israel and Iran trade strikes and counter-strikes, it has fuelled fears that a regional war could erupt amid growing instability in the Middle East.

But how likely is it that a third world war could break out?

What happened?

Key details have yet to emerge so far, but US officials said that Israel has launched a retaliatory air strike on Iran after it was bombarded with missiles and drones last week.

Sources told local media that explosions were heard close to an air base which lies north-east of the Iranian city of Isfahan, in what would be a major escalation.

Iran’s Islamic Revolutionary Guard Corps (IRGC) has claimed to have shot down several drones around the air base, according to local journalists.

Unconfirmed reports suggested that Natanz, a nuclear facility deep underground, had also been targeted. An Iranian news agency said the claim was incorrect, however.

White House and Pentagon officials are understood to be closely monitoring the situation.

Why?

Israel’s attack comes after it was targeted by hundreds of Iranian drones and rockets in an unprecedented strike on April 13.

One Israeli official downplayed the barrage, labelling it a “strategic failure” as roughly 99 per cent of the projectiles were intercepted by “Iron Dome” defences and allies including the UK and US.

However, it was significant in at least one respect – it was the first time that Israel had been targeted directly from Iranian soil.

If reports are accurate and Israel has targeted the Isfahan air base, it parallels Iran’s selection of targets on April 13. Nevatim Air Base, in the south of the country, sustained minor damage during the bombardment.

Israeli officials have been clear that an attack on Iran would take place, but have not said when and whether it would be directed at its Middle East proxy groups. Those questions have now been answered.

What happens next?

After its strike on April 13, which Iran undertook after an Israeli strike on its consulate in Damascus, its leadership said it considered the matter closed.

However, it added that if Israel retaliated, then it would respond with a “much larger” attack.

World leaders urged Benjamin Netanyahu to avoid attacking Iran and destabilising the region, highlighting the lack of damage caused by Tehran’s strike.

Iran has not yet said how it will respond to Israel’s attack.

Its bombardment on April 13 was widely telegraphed in advance and officials said it was calibrated to avoid a larger conflict breaking out.

However, Tehran may feel a need to save face, and the exchanges between the countries could tip them over from a cold war into a hot war.

Jonathan Panikoff, director of the Scowcroft Middle East Security Initiative, noted that Isfahan was home to both a nuclear facility and an international airport, and that what happens next would hinge on which had been attacked.

“Future escalation depends on target and it’s too early to know that,” he wrote on social media. “Either way, message from Israel: we can hit the nuke facility.”

What are the risks?

If the attacks between Israel and Iran continue to gain intensity, then the implications are grave – for the Middle East and the world.

Iran has a number of proxy groups in the region: in the Palestinian territories, Lebanon, Iraq, and Yemen. They fired on Israel on April 13 and would presumably do so again if a war breaks out.

Israel, meanwhile, has backing among the Western powers, as seen when they united to bring down Tehran’s barrage of rockets and drones earlier this month.

Joe Biden, the US President, is said to fear that Israel’s leadership could drag him further into a conflict in the Middle East. “Take the win,” he reportedly told Mr Netanyahu.

Iran has backing further afield too, which could lay the groundwork for a wider conflict. 

It is supported by Russia – which has used its Shahed drones to great effect to prosecute its war in Ukraine – while maintaining close ties to China.

Is World War Three going to start?

Few experts would disagree that the world today looks far more unstable that it did 10 years ago. But there is disagreement about whether a world war could happen.

Hugh Lovatt, a policy fellow at the European Council on Foreign Relations think tank, argued that the conflicts around the world are self-contained rather than connected.

“The reassuring news is we are not heading towards the Third World War,” he told Sky News.

However, others believe that the fault-lines in a potential conflict have already been drawn, with tensions growing between the democratic Western powers and autocratic regimes such as Iran, Russia and China.

With the Ukraine-Russia war entering its third year, the global order seems to be fraying. Some believe it could snap altogether, and that these conflicts – relatively confined, so far – could tip in a world war.

Grant Shapps, the Defence Secretary, has warned that in as little as five years time there could be multiple theatres of conflict spread across the globe: Russia, China, Iran and North Korea.

“The world has moved from a post-war to a pre-war era,” he added. 

Along with the Middle East, many commentators see the fate of Ukraine as key. If it falls to Vladimir Putin, it could embolden Russia to attack a Nato country, or China to invade Taiwan – which the US has pledged to defend.

Denys Shmyhal, the Ukrainian prime minister, has warned there would be a “third world war” if Kyiv falls.

Figures in Nato and western governments have predicted a war with Vladimir Putin could break out in a matter of years.

However, Edward R. Arnold, senior research fellow at the Royal United Services Institute, suggested that conflict with Russia was less likely as its armed forces were degraded by the strain of fighting in Ukraine.

“Vladimir Putin will be looking pretty closely at what happens in the Middle East,” he added.

“It’s all helping Putin at the moment because while focused on the Middle East we are not as focused as we have been on Ukraine.”