Poverty and rising violence are causing tension between southern and northern Sudan
Ten international aid groups say a 2005 peace deal in Sudan is on the verge of collapse and that the world must act now to prevent renewed conflict.
The agencies blamed a "lethal cocktail" of rising violence, chronic poverty and political tensions.
The oil-rich south is due to hold a referendum on independence in 2011.
The peace deal five years ago ended a 22-year civil war that left some 1.5 million people dead. The region remains one of the poorest areas of the world.
The peace deal saw President Omar al-Bashir's northern National Congress Party (NCP) enter government with the Sudan People's Liberation Movement (SPLM) rebels from the south.
But tensions are again rising between the former enemies in the run-up to the referendum and April's general election - the first nationwide poll for 24 years.
The SPLM has accused the NCP of stirring up ethnic violence in the south to destabilise the region ahead of the polls - charges the northern party denies.
More people died from violence in southern Sudan last year than in Darfur.
In their report, the aid agencies cite disputes over Sudan's oil resources, April's election and the independence referendum as potential flashpoints.
A return to conflict would have devastating consequences extending far beyond southern Sudan, they say.
The BBC's James Copnall in the Sudanese capital, Khartoum, says the country is clearly at the start of a highly charged and risky 12 months.
However, he says that there is a heavy international presence in the country - unlike previous crises the country has gone through.
The strength of the UN peacekeeping mission has yet to be tested, but almost 10,000 military personnel are charged with keeping the peace in the south, he says.
Sudan's ambassador to London, Omar Muhammad Siddiq, acknowledged that the situation in southern Sudan was "deteriorating".
He said communities were competing for scarce resources and were arming themselves and fighting "tribal wars".
"The situation is not as good as we were expecting after the signature of the comprehensive peace agreement," he said.
However, he argued that the unrest would not affect the election, in which he said parties and voters were preparing to participate.
Meanwhile, the UK says it has pledged £54m ($87m) in aid to help rebuild southern Sudan and prepare for April's elections.
British Foreign Office minister Glenys Kinnock, who is due to visit Sudan, noted that many Sudanese still live in poverty.
"They are doing disastrously, and that is reflected in the terrible poverty and relentless suffering of the people," she said.
But she added that fully blown conflict could still be averted.
"What we're asking is for the leadership of both sides... [to] ensure that they talk together, they work together with the same motivation, which is to bring peace and security to Sudan," she said.