Churkin said there were several unresolved issues in the UN Security Council draft.
Iran has vowed to continue its nuclear programme, which it says is for peaceful uses only, despite the resolution, even if it is approved by Russia.
Russia is building an $800 million light-water reactor for Tehran at Bushehr that is exempted in the resolution.
The draft demands Tehran end all uranium enrichment work, which can produce fuel for nuclear power plants as well as for bombs, and halt research and development that could lead to atomic weapons.
The sanctions include a ban on imports and exports of dangerous materials and technology relating to uranium enrichment, reprocessing and heavy-water reactors, as well as ballistic missile delivery systems.
The US and European drafters of the resolution - Germany, France and Britain - held out hope a vote could still be called on Friday after another round of discussions with Russia and China.
"We're close to a final text," said Alejandro Wolff, the acting US ambassador. "There are some elements that are still of concern to us (and) to other delegations.
"We're hoping for a vote as soon as possible," Wolff said. "We'll see if we can do it tomorrow [Friday]."
Qatar's permanent delegate to the UN has hinted that his country might abstain from voting.
Nasser Abdul Aziz al-Nasr, who is the head of the Security Council for December, said: "Qatar is not in favour of draft resolutions that add oil to fire but seeks a diplomatic solution."
In a concession to Moscow on Wednesday, the Europeans deleted a mandatory travel ban and instead told nations to notify a Security Council sanctions panel if any Iranians on the list transit through their countries.
The measure is a reaction to Iran's failure to comply with an August 31 UN deadline to suspend uranium enrichment work and resume negotiations.
The resolution is under Article 41 of Chapter 7 of the UN Charter, which makes enforcement mandatory but restricts action to nonmilitary measures.
It would suspend sanctions if Tehran in turn suspended "all enrichment related and reprocessing activities, including research and development."