Britain must use next month's presidency of the United Nations Security Council to "show leadership" on Sudan, the Archbishop of Canterbury has said.
Dr Rowan Williams said the situation in the African nation was "no less critical" now that preparations have begun for a referendum on independence for the south of the country.
The Archbishop said concern about how the referendum will work in the border area is growing and there are also fears of a humanitarian crisis if up to four million people of southern descent living in the north are forced out following the vote.
Dr Williams, who was joined by the Archbishop of Sudan Daniel Deng for Thursday's press briefing at Lambeth Palace, said: "The UK Government has a good record of involvement in Sudan."
Britain takes over the presidency of the UN Security Council during November and Dr Williams said: "There is a good opportunity for Britain to show leadership." He added: "I would like to see and I have confidence I will see our government stepping up to the plate and do the sort of monitoring that is needed in Sudan." He said international pressure was needed "to avoid the sort of disaster we all fear".
Dr Williams, who with Dr Deng met then Prime Minister Gordon Brown in January to discuss the African nation, said: "The situation in Sudan is no less critical than it was several months ago and, if anything, gets more serious as days go by. This is not time at all to ease up the pressure that our government can give."
Speaking about the referendum due to take place on January 9 next year, Dr Williams said "a great many of the things that should have been done in preparation have not been done".
Dr Deng, who Dr Williams described as a "colossally effective advocate for Sudan", said: "I think the international community has an obligation to make sure the referendum is done."
He spoke to send an early warning of the potential disaster ahead and "to appeal to the international community to support the people of Sudan, not to allow them to go back to war".
A vote for southern independence could lead to millions of people being "pushed" back to the region, prompting a humanitarian crisis, he said, adding: "We want the international community to be ready for that."