IAEA Director General Amano
IAEA Director General AmanoReuters

The head of the U.N. atomic agency said Thursday that while the details of a hacking incident involving one of its servers have yet to be elucidated, he was "confident" that no sensitive information related to Iran’s nuclear activities had been stolen.

"We are continuing to analyze this event and I don't claim that I have all the knowledge of what happened. We are continuing to analyze the case," said Director General of the International Atomic Energy Agency (IAEA) Yukiya Amano.

"We don't know everything but we are confident that safeguards information have not been stolen,” he said, referring to the agency’s activities in ensuring the safety and confidentiality of nuclear weapons technology and knowhow.

“But we don't know anything yet, we are analyzing it," he told a news conference.

Amano revealed that the hacking, which was first reported by the IAEA on Tuesday, had taken place several months ago, calling it "deeply regrettable".

The hacking group, calling itself Parastoo, which means "swallow" in Farsi, posted scores of email addresses of experts who have been working with the U.N. agency on a website, along with comments critical of Israel's nuclear activities.

The group said in an online statement it had "grabbed a total backup" and that it was "reassuring (the) IAEA that their critical information is safe with us".

Israel, widely assumed to have nuclear weapons but which has never confirmed or denied it, is not a signatory to the nuclear Non-Proliferation Treaty (NPT) and, unlike Iran, is not obliged to grant access to IAEA inspectors.

There has been an increase in suspected Iranian cyber attacks this year, as the regime attempts to ward of Western attempts to hinder its nuclear program.