The four men, whittled down from a longer British list, include one Sudanese government official, one pro-government militia member, and two rebel leaders, the first to be scheduled for sanctions authorised by the UN Security Council more than a year ago. The four were not identified.

Both the Russian and Chinese ambassadors said now was not the time to impose a travel ban or an assets freeze on Sudanese individuals because of the ongoing peace talks on the escalating Darfur conflict, held in Abuja, Nigeria.

Wang Guangya, Beijing's ambassador to the UN, told reporters: "China believes this is not the right moment since the Abuja negotiations are under way, and we expect progress on that [at the end of April]."

Andrei Denisov, Russia's ambassador, said: "Let's wait, at least until the end of April, and then come back to the issue. Don't do any harm to that very fragile process in Sudan."

The two envoys did not make clear if they would approve the embargoes later.

A council sanctions committee on Thursday distributed the four names for approval to all 15 council nations. Had no one objected, the list would have been adopted on Monday.

But China on Monday submitted a letter to the committee, saying the sanctions panel - and not the full council as John Bolton, the US ambassador, proposed - should discuss the issue further, diplomats said.

Russia made its objection known in a telephone call, saying it aligned itself with China.

Qatar also objects

Qatar, the only Arab member of the council, also objected, diplomats said.

"China believes this is not the right moment since the Abuja negotiations are under way, and we expect progress on that [at the end of April]"

Wang Guangya, Beijing's ambassador to the UN

However, Bolton said he wanted a resolution that would impose the sanctions, thereby forcing Russia and China, who have frequently sided with the Khartoum government, to approve, abstain or veto the action publicly.

"We've been trying to get this process in gear for a year," Bolton said. New discussions are expected on Tuesday.

"We are preparing a resolution for the full council to adopt. It would impose the sanctions." Bolton said. "It's a down payment, and certainly not the end of the sanctions process."

The Security Council approved a resolution in March 2005, calling for a freeze on assets overseas and a travel ban on individuals who defy peace efforts, violate human rights or conduct military overflights in Darfur.

Russia, China, Algeria and Pakistan abstained.

Darfur devastation

The Darfur conflict erupted in early 2003 when mostly non-Arab tribes took up arms accusing the Arab-dominated Khartoum government of neglect.

The government responded by arming mainly Arab militias, known as Janjawid, who began a campaign of murder, rape, arson and plunder that drove more than 2 million villagers into squalid camps in Darfur and in neighboring Chad. Khartoum denies responsibility.

The main bulwark against abuses in Darfur is the cash-strapped African Union which, under pressure from its Arab members who side with Khartoum, is hesitating to merge its 7,000 troops with a proposed UN force.

Sudan has not consented to an enlarged military operation.