In an interview with AFP after a year in office, IAEA Director General Rafael Grossi issued the appeal in response to calls by Iranian MPs to end inspections following the killing.

"We understand the distress but at the same time it is clear that no-one, starting with Iran, would have anything to win from a decrease, limitation or interruption of the work we do together with them," Grossi said.

Grossi, 59, confirmed that so far the IAEA had not yet received any signal from Iranian authorities that anything would change regarding inspections in the wake of the killing of Mohsen Fakhrizadeh.

Iran's parliament on Sunday demanded a halt to those inspections, signalling another potential retreat from a key commitment in its 2015 nuclear deal with world powers.

"This is not the first time that parliamentarians have expressed themselves in this way or in very similar ways," Grossi pointed out.

"We haven't received any indication of restriction or limitation of their cooperation with us," he said. "I do not see any reason to believe that this would be the case now."

Grossi emphasised that the IAEA's extensive inspections regime was "essential" if the outside world was to have assurances about the nature of Iran's nuclear programme.

Fakhrizadeh was laid to rest on Monday, three days after he was assassinated on a major road outside Tehran.

"Let me say that we abhor violence of any type, we are an international organisation for peace and security," Grossi said.

The killing could put yet more strain on diplomatic efforts to salvage Iran's 2015 nuclear deal with world powers, which has been disintegrating ever since the Trump administration withdrew from it two years ago.

- High-stakes gamble -

Iran has been one of the thorniest issues Grossi has had to tackle over an eventful year since taking office in early December 2019.

"They have a very large nuclear programme that requires as you know one of the biggest, if not the biggest efforts in terms of inspection. Without that... the instability in the region would be far higher," Grossi said.

A high point during his leadership was his trip to Tehran in August which ended in an agreement allowing IAEA inspectors access to two sites where undeclared nuclear activity may have taken place in the 2000s.

That had followed months where Tehran had denied access to the locations.

"I was served with a denial of access to two sites barely 40 days into the job, something that had never happened before in the history of the IAEA," Grossi recalls.

He admitted that some member states and analysts had thought his gambit of flying to Iran for talks was a risk.

However, it paid off and won him plaudits in Vienna's diplomatic circles.

- 'Sense of urgency' -

However, when it comes to another controversial undeclared site, in the Turquzabad district of Tehran, Grossi said there were still unanswered questions over the presence of nuclear material.

"I do not want to dramatise but it is important that we get clarification," he said.

While not setting a deadline for Iran to provide the necessary information, Grossi said "a sense of urgency is clear on my side" and recalled that the site has been under discussion for almost two years now.

Grossi said his proudest achievement was that the agency managed to keep going throughout the coronavirus despite the challenges.

"I had to argue my way with foreign ministers, I had to hire private planes to send my inspectors - it wasn't easy."

Looking to the year ahead, Grossi said he hoped the Agency would be a "priority" for the incoming administration of President-elect Joe Biden.