Iran has the capacity to start enriching uranium again - for a possible bomb - in "a matter of months", the head of the UN's nuclear watchdog has said.

Rafael Grossi, head of the International Atomic Energy Agency (IAEA), said the US strikes on three Iranian sites last weekend had caused severe but "not total" damage, contradicting Donald Trump's claim that Iran's nuclear facilities were "totally obliterated".

"Frankly speaking, one cannot claim that everything has disappeared and there is nothing there," Grossi said on Saturday.

Israel attacked nuclear and military sites in Iran on 13 June, claiming Iran was close to building a nuclear weapon.

The US later joined the strikes, dropping bombs on three of Iran's nuclear facilities: Fordo, Natanz and Isfahan.

Since then, the true extent of the damage has been unclear.

On Saturday, Grossi told CBS News, the BBC's US media partner, that Tehran could have "in a matter of months... a few cascades of centrifuges spinning and producing enriched uranium".

He added that Iran still possessed the "industrial and technological capacities... so if they so wish, they will be able to start doing this again."

The IAEA is not the first body to suggest that Iran's nuclear abilities could still continue - earlier this week, a leaked preliminary Pentagon assessment found the US strikes probably only set the programme back by months.

It is possible, however, that future intelligence reports will include more information showing a different level of damage to the facilities.

Trump retorted furiously by declaring that Iran's nuclear sites were "completely destroyed" and accused the media of "an attempt to demean one of the most successful military strikes in history".

For now, Iran and Israel have agreed to a ceasefire.

But Trump has said he would "absolutely" consider bombing Iran again if intelligence found that it could enrich uranium to concerning levels.

Iran's armed forces chief of staff Abdolrahim Mousavi said on Sunday that Tehran was not convinced Israel would abide by the ceasefire.

"We did not start the war, but we have responded to the aggressor with all our power, and as we have serious doubts over the enemy's compliance with its commitments including the ceasefire, we are ready to respond with force" if attacked again, Mousavi was quoted as saying by state TV.

Iran, on the other hand, has sent conflicting messages on how much damage was caused.

In a speech on Thursday, Iran's Supreme Leader Ayatollah Ali Khamenei said the strikes had achieved nothing significant. Its foreign minister Abbas Araghchi, however, said "excessive and serious" damage was done.

Iran's already-strained relationship with the IAEA was further challenged on Wednesday, when its parliament moved to suspend cooperation with the atomic watchdog, accusing the IAEA of siding with Israel and the US.

Tehran has rejected the IAEA's request to inspect the damaged facilities, and on Friday, Araghchi said on X that "Grossi's insistence on visiting the bombed sites under the pretext of safeguards is meaningless and possibly even malign in intent".

Israel and the US attacked Iran after the IAEA last month found Tehran to be in breach of its non-proliferation obligations for the first time in 20 years.

Iran insists that its nuclear programme is peaceful, and for civilian use only.

Despite the Iranian refusal to work with his organisation, Grossi said that he hoped he could still negotiate with Tehran.

"I have to sit down with Iran and look into this, because at the end of the day, this whole thing, after the military strikes, will have to have a long-lasting solution, which cannot be but a diplomatic one," he said.

Under a 2015 nuclear deal with world powers, Iran was not permitted to enrich uranium above 3.67% purity - the level required for fuel for commercial nuclear power plants - and was not allowed to carry out any enrichment at its Fordo plant for 15 years.

However, Trump abandoned the agreement during his first term in 2018, saying it did too little to stop a pathway to a bomb, and reinstated US sanctions.

Iran retaliated by increasingly breaching the restrictions - particularly those relating to enrichment. It resumed enrichment at Fordo in 2021 and had amassed enough 60%-enriched uranium to potentially make nine nuclear bombs, according to the IAEA.