U.S. President Donald Trump said on Wednesday that the intelligence following the strikes on Iranian nuclear sites was inconclusive, but also suggested the damage could have been severe.

"The intelligence was very inconclusive. The intelligence says we don't know. It could've been very severe. That's what the intelligence suggests," Trump told reporters ahead of meeting with world leaders at a NATO summit.

Later, during the same round of comments, Trump argued that Iran's nuclear deal had been set back "basically decades, because I don't think they'll ever do it again".

Trump insisted that US strikes resulted in the "total obliteration" of Iran's nuclear capabilities, setting the country's atomic programme back by "decades".

"They're not going to be building bombs for a long time," said Trump, who added that the ceasefire between Israel and Iran after the strikes was going "very well".

Asked if the United States would strike again if Iran rebuilt its nuclear enrichment programme Trump said: "Sure."