The world is nervously watching as the gloves come off between Iran and Israel

Where once the US would have been the brake on spikes in Syrian violence, there is a real possibility President Donald Trump's withdrawal from the 2015 Iran nuclear deal is greasing the wheels towards a wider regional war.

In recent months, the world's top diplomat, UN Secretary-General António Guterres, has warned that Israeli and Iranian tit-for-tat strikes in Syria could quickly boil over to a regional conflagration.

Overnight Wednesday, rockets fired by Iranian forces from inside Syria toward Israel triggered a forewarned robust response from Israel's military -- targeting Iranian military assets in Syria.

Since early February, when Israel says it shot down an Iranian drone laden with explosives that was launched from Syria, the Israeli Defense Forces have increased retaliatory strikes in Syria at Iranian targets.

Some of those strikes are reported to have killed several Iranian fighters. Yet until this point there had been no Iranian retaliation.

The sudden surge in the exchange of rockets Wednesday night -- on the heels of Trump's exit from the Joint Comprehensive Plan of Action -- hints that Iran has suspended its strategic restraint.

If so, the likelihood that the Iranian-Israeli confrontation will escalate increases.

In Tehran, President Hassan Rouhani warned Germany, France and the UK, that they have only "a very limited time to save the JCPOA." But he is a moderate. The Iranians fighting in Syria fall under a more hardline command.

It's their comrades who have been killed in Israeli strikes and their patience will have worn thinner than Rouhani's strategic politicking.

Most European diplomats fear that once the Trump's administration leans on European businesses hard enough, they won't be able to plug the economic shortfall, something Rouhani needs so he can sell the Iran deal without America at home.

In short, the gloves in a potential Israel-Iran confrontation are coming off. The question is this: were Wednesday night's strikes the opening salvo, or a sign of what is to come?

President Emmanuel Macron of France fears the former. His staff in Paris say he is pushing for calm: "He calls for de-escalation and he will talk about this with the German Chancellor today."

Israeli Defense Minister Avigdor Liberman said on Thursday morning that most of Iran's infrastructure in Syria was hit and that he hopes this chapter of "Iranian radicalism" is over. But indicating that what happens next is down to Iran, he added: "If it will rain in Israel, there will be a biblical flood on the other side."

In Damascus, a Greek reporter asked President Bashar al-Assad if Syria would be the venue for world war three. His response: "No, for one reason: because fortunately, you have a wise leadership in Russia."

Putin -- as many international diplomats have warned could happen -- finds himself, absent a working peace plan in Syria, riding a tiger. A bigger war in Syria would require a bigger military spend from him -- something that would further strain his own stretched economy.

Recently reelected, he has plenty of political capital but not a lot of real cash to spare. US and European sanctions have been eating a hole in Russia's pocket. The ruble has had a rocky ride in recent months.

During his Wednesday visit to the Kremlin, Israeli Prime Minister Benjamin Netanyahu is understood to have warned Putin about strikes on Iran's military assets inside Syria.

As Iran is Russia's principal ally keeping Assad in power, Moscow is very carefully tracking Israel's every move.

For whatever reason, Putin appeared willing to see Iran hit, knowing the straining and destabilizing effect it may have on their alliance backing Assad.

That Netanyahu, Trump's most ardent supporter in dumping the JCPOA, was in Moscow the day before the attack signals many things -- not least the dangerous complexity of having so many powers at play in such a confined conflict. But it also emphasizes the diminishing US influence in Syria -- and the region in general.

In Riyadh on Wednesday, Saudi Arabian Foreign Minister Adel al-Jubeir reiterated his country's warnings about Iran's nuclear ambitions, saying: "We have made it very clear that if Iran acquires nuclear capability we will do everything we can to do the same."

After Israel, the Saudis are the biggest backer of Trump's decision to pull out of the JCPOA. They fears growing Iranian influence in the region -- not just to their north in Syria and Iraq, but over their southern border in Yemen.

On Wednesday, Iranian-backed Houthi rebels, who tossed Yemen's internationally recognized government from power four years ago, fired long-range ballistic missiles into Saudi. One was reportedly shot down by a US-made Saudi counter-missile battery just outside the capital Riyadh.

In recent months, Houthis have stepped up missile attacks targeting Riyadh. None have gotten through so far. But patience in Riyadh is running thin -- the expectation there is that Trump's exit from the JCPOA could signal a ramped-up Saudi targeting of Houthi leaders.

How Iran would handle its Houthi proxies in this case is unclear. But international concern has been growing, particularly over the past week, as the Saudi-led coalition's airstrikes in Yemen have allegedly hit several civilian targets recently.

In pulling out of the Iran nuclear deal, Trump hinted at the peace benefit for the region: "If I allowed this deal to stand, there would soon be a nuclear arms race in the Middle East. Everyone would want their weapons ready by the time Iran had theirs."

While no one expected those lofty long-term goals realized already, just two days later, most diplomats hoped the lid could be kept on tensions until everyone outside the White House could figure out the next step forward.

There was no "plan B." It's being made up on the fly, with no guarantees hardliners don't derail the world's diplomats.

Escape routes are still open, but the fog and consequences of sudden conflict may soon shut them down.

Today, it's still possible -- albeit highly improbable -- that should Trump decide, he could give European businesses "cutouts" and allow them to continue working in Iran; then maybe Iran's moderates can buy more time and rein in their hardliners before it's too late.

But the reality is, exiting the JCPOA has ushered in a new era of international relations where the unexpected and unpredictable have a far greater possibility of rapidly outpacing common sense and routine diplomacy.