Iran's Supreme Leader Ayatollah Ali Khamenei said his country had delivered a "slap to America's face" with its strike on a US airbase in Qatar, and warned against any further attacks in his first public comments since a ceasefire was declared with Israel after 12 days of war.

Khamenei spoke in a recorded video broadcast on Iranian state television, his first appearance since June 19. The 86-year-old, a skilled orator known for his forceful addresses to the country's more than 90 million people, appeared and sounded more tired than he had just a week ago, speaking in a hoarse voice and occasionally stumbling over his words.

The speech, which went on for more than 10 minutes, was filled with warnings and threats directed toward the United States and Israel, the Islamic Republic's longtime adversaries.

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The supreme leader downplayed the US strikes on three Iranian nuclear sites using bunker-buster bombs and cruise missiles, saying that US President Donald Trump – who said the attack "completely and fully obliterated Iran's nuclear program – had "exaggerated" its impact.

"They could not achieve anything significant," Khamenei said.

Missing from his video message was any mention of Iran's nuclear program and the status of their facilities and centrifuges following extensive US and Israeli strikes.

His characterization of Iran's strike on a US airbase in Qatar contrasted with US accounts of it as a limited attack with no casualties.

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The head of the UN nuclear watchdog, International Atomic Energy Agency Director Rafael Grossi, reiterated that the damage done by Israeli and US strikes at Iranian nuclear facilities "is very, very, very considerable."

"I think annihilated is too much, but it suffered enormous damage," Grossi said.

Iran's Foreign Ministry spokesman, Esmail Baghaei, earlier this week also conceded that "our nuclear installations have been badly damaged, that's for sure."

Khamenei has not been seen in public since taking shelter in a secret location after the outbreak of the war when Israel attacked Iranian nuclear facilities and targeted top military commanders and scientists.

Following the US attack on Iran's nuclear facilities, Trump was able to help negotiate a ceasefire that came into effect on June 24.

Iranian leader warns US against further attacks

Khamenei claimed the US had only intervened in the war because "it felt that if it did not intervene, the Zionist regime would be utterly destroyed."

"It entered the war to save them, yet it gained nothing," he said.

He said his country's attack on the US base was significant, since it shows Iran "has access to important US centres in the region and can act against them whenever it deems necessary."

"The Islamic Republic was victorious and, in retaliation, delivered a hand slap to America's face," he said, adding, "This action can be repeated in the future."

"Should any aggression occur, the enemy will definitely pay a heavy price," he said.

Trump has dismissed the retaliatory attack as a "very weak response," saying that the US had been warned by Iran in advance and stressing that there had been no casualties.

Since the ceasefire, life has been gradually returning to normal in Iran. The country has partially reopened its airspace, which had been shut down since the war began, and shops in Tehran's capital began to reopen, with traffic returning to the streets.

Majid Akhavan, spokesperson for the Ministry of Roads and Urban Development, said Iran had reopened its airspace for the eastern half of the country to domestic and international flights, including those transiting Iranian airspace.

Tehran tenants repair homes damaged by Israeli airstrike. – Reuters

Earlier this week, Tehran said 606 people had been killed in the conflict in Iran, with 5332 people wounded. The Washington-based Human Rights Activists group has released figures suggesting Israeli strikes on Iran had killed at least 1054 and wounded 4476.

The group, which has provided detailed casualty figures from multiple rounds of unrest in Iran, said 417 of those killed were civilians and 318 were security forces.

At least 28 people were killed in Israel and more than 1000 wounded, according to officials there. During the 12-day war, Iran fired more than 550 missiles at Israel with a 90 per cent interception rate, according to new statistics released by Israeli authorities. Israel, meantime, hit more than 720 Iranian military infrastructure targets and eight nuclear-related sites, it said.

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Trump has also asserted that American and Iranian officials will talk next week, giving rise to cautious hope for longer-term peace.

Iran has not acknowledged that any such talks would take place, though US Mideast envoy Steve Witkoff has said there has been direct and indirect communication between the countries. A sixth round of US-Iran negotiations was scheduled for earlier this month in Oman but was cancelled after Israel attacked Iran.

Iran has insisted that it will not give up its nuclear program. In a vote underscoring the tough path ahead, its parliament has agreed to fast-track a proposal that would effectively stop the country's cooperation with the IAEA, which has monitored the program for years.