Russia and China have criticised a UN Security Council draft resolution on Iran's nuclear ambitions.
Tehran says the West is trying to bully it into action
Russia says the draft needs rewriting with stronger emphasis put on building confidence between Iran and the UN.
China says it is worried that the draft's Western sponsors have based it on UN rules that could open the way for the use of military force against Iran.
The draft demands that Iran stop nuclear enrichment and threatens further measures if it does not do so.
Chapter Seven threat
Iran insists its nuclear programme is for peaceful proposes only.
However, Western nations are concerned it is seeking a nuclear weapons capability.
The five permanent members of the UN Security Council are due to meet informally on Saturday to try to thrash out their differences over the draft, drawn up by Britain and France, with US backing.
Russian Deputy Foreign Minister Sergei Kislyak was quoted by Russian media as saying that the draft needed "major changes" and that negotiations over the text were "ongoing".
Russia's UN Ambassador Vitaly Churkin went further saying that Moscow opposes the push for the resolution to be adopted under Chapter Seven of the UN Charter, which could, after further decisions, allow for sanctions or even military action.
China also objects to the use of Chapter Seven, and is concerned by the phrasing of the draft which says that the "proliferation risk" posed by Iran is a threat to international peace and security.
Russia and China have also complained about a section of the draft text which calls on countries to stop selling technology to Iran that could help its nuclear programme. This, they say, is sanctions by another name.
The Security Council members backing the resolution had hoped the Council would adopt the resolution before foreign ministers meet in New York on Monday.
But, the BBC's UN correspondent Laura Trevelyan says that the comments from Moscow and Beijing, who both wield a veto in the Security Council, make agreement very unlikely.
On Friday Iran accused the US and its allies of creating an artificial crisis by tabling the UN resolution.
Iran's envoy to the UN, Javad Zarif, called for a "serious, reasonable" debate instead while President Mahmoud Ahmadinejad said his country was being "bullied".
Mr Zarif told reporters the document was regrettable because there were a "multitude of possibilities for finding a peaceful resolution". Those who drafted it, he said, showed an "intention to create a crisis where a crisis is not needed".
He reiterated Tehran's basic position, that it will not stop enrichment because it intends to produce electricity, not nuclear bombs.
Speaking at a summit of mainly Muslim states in Baku, Azerbaijan, the Iranian president said that "certain bullies" were "insolently trying to interfere in the internal affairs of other countries".
"We intend to continue our activity... until we manage industrial-scale production of nuclear fuel for our atomic power stations," Mr Ahmadinejad told the meeting of the 10-strong Economic Cooperation Organisation group.