Russia and China say they will oppose UN sanctions against four Sudanese officials accused of involvement in continuing violence in Darfur.
Both rebels and government officials are threatened with sanctions
Russia's UN envoy said the Security Council should delay sanctions until Sudan's talks with Darfur rebels reach an African Union deadline of 30 April.
The Chinese UN envoy also said the time was not right for the measures proposed by the UK and the US.
Some 2m people have fled their homes in Darfur in what the US says is genocide.
Sudan's government denies arming Arab militias to drive black Africans from their homes after two rebel groups took up arms three years ago.
Sudan accuses the US of wanting to impose sanctions and exaggerating the scale of the problems in Darfur for political reasons.
Russia and China have long opposed sanctions against Sudan. Both have strong trade links with Khartoum.
The four men threatened with a travel ban and a freeze on their assets held abroad include one Sudanese government official, one pro-government militia member, and two rebel leaders.
US ambassador to the UN John Bolton said he had requested a meeting of the Security Council to discuss the issue.
Peace talks between Sudan and the Darfur rebels, convened by the African Union, have been taking place in the Nigerian capital, Abuja, over the past two years.
The end of April has been set as a deadline for an agreement in Abuja.
"China believes this is not the right moment since the Abuja negotiations are under way, and we expect progress on that," said Chinese UN ambassador Wang Guangya.
Russian ambassador Andrei Denisov also said sanctions should not be imposed before the end of April.
"Don't do any harm to that very fragile process in Sudan," he said.