VIENNA/tehran - The chief of inspections at the UN nuclear watchdog has resigned suddenly, the agency said Friday without giving a reason.

The departure of Tero Varjoranta comes at a sensitive time, three days after the United States announced it was quitting world powers’ nuclear accord with Iran, raising questions as to whether Tehran will continue to comply with it.

Varjoranta, a Finn, had been a deputy director general of the International Atomic Energy Agency and head of its Department of Safeguards, which verifies countries’ compliance with the nuclear Non-Proliferation Treaty, since October 2013. He will be replaced in an acting capacity by the head of the department’s Iran team, the Vienna-based IAEA said.

“Mr. Tero Varjoranta has resigned effective May 11, 2018,” an IAEA spokesman said. “The director general has appointed Mr. Massimo Aparo, acting director, Office for Verification in Iran, as acting deputy director general and head of the Department of Safeguards, effective immediately.”

The accord signed by Iran and major powers in 2015 imposed strict limits on Iran’s atomic activities to help ensure they are not put to developing nuclear bombs in exchange for the lifting of international sanctions against Tehran. The IAEA is policing those restrictions and said on Wednesday, the day after Trump’s announcement, that Iran was still implementing its commitments under the deal.

The UN watchdog has also repeatedly defended the landmark agreement, saying it is a gain for nuclear verification. “The agency’s safeguards activities will continue to be carried out in a highly professional manner,” the spokesman said.

Asked why Varjoranta had resigned, he said: “The agency cannot comment on personnel matters, which are confidential.” IAEA Director General Yukiya Amano plans to appoint a permanent replacement as soon as possible, he added.

Meanwhile, Iran's foreign minister will embark on a diplomatic tour to try to salvage the nuclear deal amid high tensions following the US withdrawal and global fears over reports of unprecedented clashes with Israel in Syria. Mohammad Javad Zarif will leave late Saturday for visits to Beijing, Moscow and Brussels, a spokesman said Friday, holding meetings with all five of the remaining parties to the 2015 nuclear deal.

Iran appeared determined not to be drawn into a wider regional conflict with Israel during the sensitive negotiations. That is despite Israel's claims it struck dozens of Iranian targets inside Syria early on Thursday as part of "Operation House of Cards".

Israeli Defence Minister Avigdor Lieberman urged Syrian President Bashar al-Assad to "throw the Iranians out" of his country. Israel said the strikes were in response to a missile volley fired from southern Syria by Iran's Quds force, that struck the occupied Golan Heights without causing casualties.

But Iran flatly denied the Israeli version of events, saying Israel's attacks were carried out on false "pretexts".

"The repeated attacks by the Zionist regime on Syrian territory were carried out under pretexts that were invented by themselves and are without foundation," said foreign ministry spokesman Bahram Ghasemi, without offering further details. Iran must tread a delicate line as it seeks to show resolve against Trump and the Israeli strikes without alienating the European partners it needs to salvage something from the nuclear deal.

Zarif will hold high-pressure talks with the other parties to the deal, first in Beijing and Moscow, and then with his counterparts from Britain, France and Germany in Brussels on Tuesday.

All five have condemned Trump's move to walk out of the deal and reimpose crippling sanctions, but European companies in particular will be highly vulnerable to economic pressure from Washington.

France still hopes for a wider settlement that will cover Iran's activities across the Middle East, and warned Tehran on Thursday "against any temptation for regional dominance". Iran's hardliners are already mobilising against any concessions to Europe, with hundreds protesting in Tehran after Friday prayers, saying it was time to abandon the deal.

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

In Jerusalem, around 200 Jews gathered at the Western Wall for prayers "against the enemy".

"We came here to pray to God after the victory against Iran" following the US withdrawal from the nuclear deal, said Aryeh Stern, a rabbi from Jerusalem.

Southern Syria was quiet but tense, with monitors saying Syrian, Iranian and allied Lebanese forces from Hezbollah were on high alert.

The Israeli raids had prompted concern Iran could activate its powerful ally Hezbollah to retaliate from its positions in southern Lebanon, opening up a deadly new front in the conflict.

Iranian analysts said Israel had struck first on Thursday, and that any retaliation was the work of the Syrian military, not Iran. "The Israelis want to make this into an Iran-Israel thing, but it isn't. Whatever happens in Syria happens under the command of the Syrians," said analyst Mohammad Marandi, who was part of Iran's negotiation team leading up to the nuclear deal.

Analysts say Israel feels it has a green light from Washington to move more aggressively against Iran's presence in Syria, particularly after Trump's withdrawal from the nuclear deal. They also see a rare chance for Iran to hold the moral high ground.

"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 Affairs in Paris.

Russia - which is alone in having close relations with both Iran and Israel - has sought to position itself as a mediator to prevent further escalation.

Its foreign minister Sergei Lavrov said "all issues should be solved through dialogue" and that Russia had warned Israel to avoid "all actions that could be seen as provocative".

However, one analyst at London's Chatham House, Yossi Mekelberg, said the strikes on Iranian targets "were likely undertaken with tacit Russian approval".

"Russia is not happy with Iran gaining too much power, too much influence there," he said.

On Friday the Kremlin said Russian President Vladimir Putin had spoken with Germany's Angela Merkel and Turkey's Recep Tayyip Erdogan in a bid to keep the Iran nuclear deal alive.

"The importance of preserving the deal from a point of view of international and regional stability was highlighted," it said.