By Imogen Foulkes BBC News, Geneva

Mark Malloch Brown (l) says members must be committed

The UN's deputy secretary general says member states must renew their commitment to the United Nations or risk tearing it apart.

Mark Malloch Brown said deep divisions within the UN, primarily over the conflict in Iraq, were hindering crucial reforms of the organisation.

But the US assistant secretary of state for international affairs said blaming Iraq for the UN's problems was unfair.

The UN is deep into a reform process that was agreed last year.

Divided aims

The creation of a new human rights body has already been achieved after some bitter wrangling.

But now big divisions are emerging in other areas.

Crucial management changes, for example, or expansion of the Security Council.

I think it's unfair to characterise the poisonous atmosphere as strictly the product of the Iraq war Mark Lagon, US assistant secretary of state for international affairs

Mr Malloch Brown said the debate had turned into what he called "a knock down, drag out bar room brawl".

"The real background to that is this very divided membership since Iraq," he said.

"We've got to encourage member states to come back to renew their vows to the organisation... We need member states to do this because they are tearing this organisation apart," he said.

Mr Malloch Brown also said the UN must return to its spirit of universality and warned that powerful countries could not expect to dominate.

Mark Lagon, US assistant secretary of state for international affairs, agreed relations between UN members were bad, but denied it was all down to Iraq, and said it was in part, over reform issues.

There has been some agreement on the future of the Security Council

"I think it's unfair to characterise the poisonous atmosphere as strictly the product of the Iraq war.

"Yes, indeed it was controversial. But the poisonous atmosphere... has a larger context and the United States is not the bull in the china shop that is singularly causing this."

Where there is agreement at least is that the UN Security Council should expand.

The five permanent members should no longer reflect the victorious powers of World War II.

But there is no agreement on who might join this privileged group, how big a new council should be, or how members should be selected.