British delegates walked out of a speech by Iranian President Mahmoud Ahmedinejad at the United Nations, in which he attacked the US and Israel’s nuclear programmes at a session on nuclear proliferation.

The US Department of Defence used the same meeting to call for transparency about nuclear arms – revealing it has 5,113 nuclear weapons currently in its arsenal.

Delegates from the UK, US, France, Hungary, New Zealand and Holland at the Nuclear Non-Proliferation Treaty (NPT) conference left the room as Mr Ahmedinejad denied that Iran was building nuclear weapons.

A spokeswoman for the Board of Deputies said that they were greatly encouraged by the walk out by the British delegates and that they had made clear their concerns about Iran to the Foreign Office before Britain attended the meeting.

Mr Ahmedinejad said: “The United States has threatened to use nuclear weapons against other countries, including my country. The Zionist regime, too, continuously threatens other Middle Eastern countries.”

He called nuclear weapons “disgusting and shameful” yet appeared to criticise the UN for encouraging the use of nuclear power and for allowing a double standard in nuclear weapons programmes in the West.

US Secretary of State Hillary Clinton warned that Iran had to be held to account for continually misinforming the world about its nuclear developments.

Mrs Clinton said: "It has defied the UN Security Council and the IAEA and placed the future of the non-proliferation regime in jeopardy, and that is why it is facing increasing isolation and pressure from the international community."

She revealed the huge nuclear arsenal held by the United States, in a move which she said would improve transparency and encourage other states to do the same.

She said: "So for those who doubt that the United States will do its part on disarmament, this is our record, these are our commitments and they send a clear unmistakable signal."

No Israeli representatives attended the conference, as Israel has not signed the Nuclear Non-Proliferation treaty.

Many of the other speakers at the conference called for tougher sanctions against Iran and condemned Western companies who conduct business with the country.