The Iranian president's remarks at the UN general assembly prompted a series of walk-outs led by US delegates guardian.co.uk

President Mahmoud Ahmadinejad of Iran has accused the US government of orchestrating the 9/11 attacks to prop up Israel.

Speaking at the UN general assembly, just a few miles away from the still open wound of Ground Zero, he prompted a walkout from the chamber of delegates from the US and well as those of the UK and other European Union members. US diplomats dismissed his comments as "abhorrent and delusional".

At a time when Iran is being squeezed by sanctions imposed through the UN, Ahmadinejad showed no desire to extend a placatory hand and instead opted to repeat several old conspiracy theories relating to the terrorist attacks on September 11 2001. One theory of what happened on that day, he said, was "the US government orchestrated the attack in order to save the Zionist regime in the Middle East".

Addressing representatives of the UN's 192 member countries, the president said there was evidence that the US government had at least supported the attacks, including passports in the rubble of the Twin Towers of men who had been involved with US officials, while no trace of the alleged suicide attackers was retrieved.

Ahmadinejad's 9/11 comments will hardly be seen as providing hope for a diplomatic way out of the impasse over Iran's nuclear programme. Earlier, US president Barack Obama had demanded that Iran meet its obligations in international conventions and "confirm to the world the peaceful intent of its nuclear programme".

The Iranian leader said he remained "ready for a dialogue based on respect and justice" and for a "free debate with American statesmen".

But he went on to warn that if the security council of the UN continued to use "intimidation and sanctions" it would destroy its own remaining credibility.

The theory that 9/11 was the act of a US agent provocateur, or even of George Bush himself, has long been one of the most prevalent conspiracy theories relating to the attacks. Ahmadinejad compared the almost 3,000 people who died on 9/11 to the hundreds of thousands who had been killed in Iraq and Afghanistan.

• This article was amended on 24 September 2010 to make clear that other EU members joined in the walkout along with the UK.