Tensions between arch enemies Israel and Iran are soaring after the biggest Israeli intervention in Syria to date, a retaliation for what it said was the first ever direct fire on its troops from Iranian forces.

At least 23 soldiers are thought to have died in the unprecedented Israeli airstrikes just after midnight on Thursday, which the Israel Defence Force (IDF) said targeted almost all of Tehran’s military infrastructure inside the war-torn country.

Israel attack Iran targets in Syria: overnight airstrike in pictures Show all 10 1 /10 Israel attack Iran targets in Syria: overnight airstrike in pictures Israel attack Iran targets in Syria: overnight airstrike in pictures Missiles rise into the sky as Israeli missiles hit air defense position and other military bases, in Damascus Syrian Central Military Media, via AP Israel attack Iran targets in Syria: overnight airstrike in pictures Missile fire is seen from Damascus Reuters Israel attack Iran targets in Syria: overnight airstrike in pictures An Israeli flag is seen placed on Mount Bental in the Israeli-annexed Golan Heights. Israel's army said today it had carried out widespread raids against Iranian targets in Syria overnight after rocket fire towards its forces it blamed on Iran, marking a sharp escalation between the two enemies. Israel carried out the raids after it said around 20 rockets, either Fajr or Grad type, were fired from Syria at its forces in the occupied Golan Heights at around midnight. AFP/Getty Israel attack Iran targets in Syria: overnight airstrike in pictures The Israeli military on Thursday said it attacked "dozens" of Iranian targets in neighboring Syria in response to an Iranian rocket barrage on Israeli positions in the Golan Heights AP Israel attack Iran targets in Syria: overnight airstrike in pictures Israeli artillery deployed missiles toward Syrian military targets, on the Golan Heights EPA Israel attack Iran targets in Syria: overnight airstrike in pictures Missile fire is seen over Daraa Reuters Israel attack Iran targets in Syria: overnight airstrike in pictures Air defence systems intercepting Israeli missiles over Syrian airspace AFP/SANA Israel attack Iran targets in Syria: overnight airstrike in pictures Israeli soldiers walk among armored vehicles in the Israeli-occupied Golan Heights Reuters Israel attack Iran targets in Syria: overnight airstrike in pictures Syrian air defense missiles are seen in the sky over the capital Damascus EPA Israel attack Iran targets in Syria: overnight airstrike in pictures Air defence systems intercepting Israeli missiles over Syrian airspace. Israeli missile strikes fired at Syria hit military bases, as well as an arms depot and military radar. AFP/SANA

The altercation comes just days after US President Donald Trump announced his country would withdraw from the landmark 2015 nuclear agreement between Iran and six world powers – a move widely viewed as a victory in Israel, which opposed the deal, and as a disaster in Iran.

What happened?

The IDF said 20 Fajr or Grad missiles were fired by the Iranian Revolutionary Guards’ al Quds Force at its positions in the Golan Heights border area late on Wednesday.

There has been no official comment from Tehran, although Lebanon's al Manar TV quoted the vice president of Iran's National Security Committee as saying, “Iran has no relation to the missiles that hit the enemy entity yesterday.”

Sana, Syria's state news agency, said the hostilities were triggered by Israeli fire over the border – something which has not happened since 1974.

So did Iran do it?

Tensions between Iran and Israel over the presence of Iranian troops and allied Hezbollah, which fight alongside Syrian President Bashar al Assad, have been building since the beginning of the year.

In February, Israel accused Iran of sending an armed drone into its territory, after which an Israeli plane was shot down while bombing positions in Syria – the first time the country had lost an aircraft in combat in 35 years. Israel has since retaliated with bolder strikes on Iranian positions in Syria which have killed at least 13 Iranian nationals.

Tehran has vowed the attacks won’t go unpunished but its military capabilities are limited. It also needs the goodwill of the international community as it struggles to save the 2015 nuclear deal, which lifted crippling sanctions, said Holly Dagres, an Iran analyst and curator of the Iranist newsletter.

“There are two big questions that come to mind: Why such a small scale attack, and why right after Trump’s decision and while Tehran is looking for European support to stay in the [nuclear deal]?” she told the Independent.

“Iran has not commented on the attack thus far. This delay could mean a couple of things. That the [Iranian] administration was taken by surprise, and that this was a Quds Force initiative without their consent. Or, Iran is making good on a threat that it would retaliate.”

Mahan Abedin, an analyst of Iranian politics, shared Dagres’ scepticism.

“The rocket fire was too weak to amount to a genuine Iranian retaliation for repeated strikes by Israel against Iranian assets … I believe the Iranian response will be harsher.”

What happens next?

The Syrian foreign ministry said the incident marked the beginning of a “new phase” in the war against Israel – but to date, Iran has not retaliated after the deaths of scores of its citizens killed by Israeli strikes in Syria.

Abedin said that Israeli Defence Minister Avigdor “Lieberman's claim to have ‘destroyed’ all of Iran's military infrastructure in Syria is clearly hyperbolic. However, he is right in describing the skirmish as the latest ‘round’ of the conflict. There is plenty of scope for escalation.”

“Now that the US is out of the [Iran deal], unfortunately, both Iran and Israel are freer to attack each other directly. My hope is that this can be contained but it is very worrisome and totally predictable after Trump's reckless action,” said Barbara Slavin, director of the Future of Iran Initiative at the Atlantic Council.

Corbyn leads debate into Parliament vote on Syria strikes: 'The government is attempting to overturn a democratic advance'

The harsh rhetoric from the US and Israel in the face of what both called an Iranian “provocation” suggests that those two parties are “working hand in glove to escalate the military confrontation,” said Dr Roham Alvandi, a professor at the London School of Economics.

Mr Trump and Israeli Prime Minister Benjamin Netanyahu hope to “provoke the Iranian leadership into taking action that will isolate and ultimately weaken the Islamic Republic,” he added.