"We were attacked in the midst of an ongoing diplomatic process," Foreign Minister Abbas Araghchi told the UN Human Rights Council in Geneva ahead of a crunch meeting with European foreign ministers.

Araghchi, making his first trip abroad since the strikes began, denounced Israel's attack as an "outrageous act of aggression".

US Special Envoy Steve Witkoff had planned to meet Araghchi in Oman on June 15 but the meeting was cancelled after Israel began the strikes days before.

"We were supposed to meet with the Americans on 15 June to craft a very promising agreement for peaceful resolution of the issues fabricated over our peaceful nuclear programme," said Araghchi.

"It was a betrayal of diplomacy and unprecedented blow to the foundations of international law," he said.

Israel began its campaign on Friday saying the operation was aimed at halting Tehran from obtaining an atomic bomb, an ambition Iran denies having.

Iran said Sunday that Israeli strikes had killed at least 224 people, including military commanders, nuclear scientists and civilians. It has not issued an updated toll since then.

Iranian strikes launched in response have also caused damage in Israel, where at least 24 people have been killed and hundreds wounded, according to the government.

Araghchi described the attacks by Israel as an "unjust war imposed on my people" that had killed "hundreds".

Pointing to the risk of radiation after strikes on atomic plants, he said: "Attacks on nuclear facilities are grave war crimes."

"Iran rightfully expects each and everyone of you to stand for justice and rule of law," he added.