Mohammad Javad Zarif's tour starts two days after unprecedented Israeli strikes in Syria which a monitor said killed at least 11 Iranian fighters, triggering fears of a broader conflict between the two arch-enemies.

He will visit Beijing, Moscow and Brussels, a spokesman said, holding meetings with all of the remaining parties to the 2015 agreement.

Before leaving, Zarif published a government statement on his Twitter page, slamming the "extremist administration" of US President Donald Trump for abandoning "an accord recognised as a victory of diplomacy by the international community".

It reiterated that Iran was preparing to resume "industrial-scale" uranium enrichment "without any restrictions" unless Europe provided solid guarantees that it could maintain trade ties despite renewed US sanctions.

Trump hit back Saturday evening, tweeted that the accord had failed to contain Iran's militarism.

"Iran's Military Budget is up more than 40 percent since the Obama negotiated Nuclear Deal was reached...just another indicator that it was all a big lie," he wrote.

Zarif's delicate diplomatic mission was complicated by reports of clashes between Iranian and Israeli forces in Syria on Thursday.

The Syrian Observatory of Human Rights said Saturday that 11 Iranians were among the pro-regime fighters killed in strikes by Israel, which has vowed to prevent Iran gaining a military foothold in neighbouring Syria.

"Six Syrian soldiers and 21 foreign fighters, including 11 Iranians" were among the dead, said Observatory director Rami Abdel Rahman.

Tehran, which has sought to avoid an escalation in regional conflict that could alienate its European partners, has not commented on whether its forces were hit.

Israel and its allies have blamed the Iranian Revolutionary Guards for initiating Thursday's exchange by launching missiles into the occupied Golan Heights.

The White House backed Israel's claims, accusing Iran of "reckless actions" that posed a "severe threat" to stability in the Middle East.

Iran denies that version of events, saying the Israeli strikes were launched on "invented pretexts".

- Diplomats fume at Trump -

Meanwhile, European diplomats in Tehran fumed that Trump's decision to withdraw from the nuclear deal could undermine years of patient work to restore commercial and diplomatic ties with the Islamic Republic.

"Since the signing of the JCPOA (nuclear deal), we have gone from an atmosphere like a gold rush, to one of utter depression," said a Western trade diplomat on condition of anonymity.

"We are waiting now for how the decision-makers in the European Union will react. If the EU leans towards accommodating the US, all the progress we have made since 2015 will be lost."

But she emphasised that many of the problems began long before Trump's move last Tuesday.

"Decisions on the Iranian side took longer than expected, international banks were reluctant to work with Iran and the recent decline in the value of (Iran's currency) made international business even more difficult," she said.

Iranian hardliners -- who have long opposed President Hassan Rouhani's moves to improve ties with the West -- are already mobilising against the efforts to save the nuclear deal.

"Officials shouldn't trust France and Britain. They will never abandon the US for us," said housewife Poormoslem at a protest rally against Trump on Friday.

A photo on the official Instagram site of supreme leader Ayatollah Ali Khamenei showed him reading a Farsi translation of Michael Wolff's scabrous account of the Trump White House, "The Fire and the Fury", quickly picking up more than 100,000 likes.

Khamenei said this week he is highly doubtful that Europe will provide the "real guarantees" needed for Iran to stay in the nuclear deal.

But analysts said Iran was determined to maintain the moral high ground in the coming weeks.

"For the first time, Iran has the chance to show the world they are not the rogue nation they are always presented as, that they negotiated in good faith and keep to their commitments," said Karim Emile Bitar of the Institute for International and Strategic Studies in Paris.

The challenge for Rouhani is to maintain his diplomatic efforts in the face of mounting challenges at home, where Iranians were already suffering high unemployment and inflation before Trump's decision.

Many say sanctions allow the government to blame outsiders for its own bad decisions.

The Western trade diplomat gave the example of Iran's recent restrictions on transferring funds to the EU -- an effort to control the rapid slide of the rial -- that caused huge problems for importers.

"It's really annoying that the Iranian government is never blamed for the really bad decisions they have taken lately concerning business, and only the sanctions are blamed," she said.

burs-ia/mdl