George Bush, the US president, responded to the assessment on Tuesday by saying that Iran remained a danger if it mastered the knowledge to make a nuclear weapon.
"Iran was dangerous, Iran is dangerous and Iran will be dangerous if they have the knowledge necessary to make a nuclear weapon," he said.
But buoyed by the US report, Ahmadinejad vowed not to roll back Iran's nuclear programme.
"If you want to start a new political game, the united Iranian nation will resist you and will not retreat one step from its programme," he said.
"We will continue our nuclear programme and we will not give it up."
Alireza Ronaghi, Al Jazeera's correspondent in Tehran, said the Iranians held the belief that they were right from the beginning.
"Many have said that Bush and the United States are the main losers following the publication of the report," he said.
"The president [Ahmadinejad] also said that if Western powers continue to insist that Iran poses a threat, it is not Iran's problem."
Push for sanctions
Before the report was made public, the five permanent UN Security Council members - the US, Russia, China, Britain and France - as well as Germany, were discussing a third round of sanctions over Iran's refusal to halt uranium enrichment.
But Wang Guangya, the Chinese ambassador to the UN, said the six powers' bid for new sanctions against Iran could be called into question by the US intelligence assessment.
"I think council members will have to consider that, because ... now things have changed," he said.
China and Russia have been reluctant to join UN sanctions actions against Iran.
Sergei Lavrov, Russia's foreign minister, said that Moscow was still urging Iran to halt enrichment, but he also suggested that the report would weigh against the sanctions resolution being pushed for by the US.
"We will judge the situation around the idea of a new UN Security Council resolution on the basis of all factors, including, of course, on the basis of public confirmation of the US information," RIA Novosti news agency quoted him as saying.
Israel, the only country in the Middle East believed to have a nuclear arsenal, questioned the findings of the US National Intelligence Estimate, saying that efforts to curb Iran's nuclear programme should continue regardless.
"The way to stop Iran is by more effective sanctions," Tzipi Livni, Israel's foreign minister, said during a news conference in Slovenia.
"Iran with a nuclear weapon is something that the world cannot afford. It is clearly a threat to the region ... While we are talking, here at this press conference, Iran continues with its enrichment activities," she said.