Fears of an escalation of bloodshed in the western region of Sudan came amid claims that the Khartoum government was moving its weapons from the south.
Jan Pronk, the UN special envoy to Sudan, called for more police, human rights monitors and African Union (AU) peacekeepers to be sent to Darfur to stem the surge in violence.
He told the UN Security Council that arms were flooding into the region, fighting was spreading beyond camps for the homeless, banditry was on the rise and rebels were staging attacks near oil facilities.
Mr Pronk’s concerns were echoed by rebel leaders in the region, who accused Khartoum of redeploying soldiers not needed after the peace deal with the south to the civil war in Darfur.
Colonel Omar Adam, the rebel leader of the Justice and Equality Movement, said "the government is preparing for war", adding that he has seen heavy and light weaponry arriving in Darfur.
Speaking after arriving in New York from Nairobi, where the peace agreement between the government and southern rebels was signed on Sunday, Mr Pronk said: "We may move into a period of intense violence unless swift action is taken.
"I do not exclude the possibility that the signature of the agreement [on the south] will be followed in the short term by an intensification of violence in and around Darfur."
Mr Pronk urged a ceasefire in Darfur and said there was "political momentum" to end the conflict, but it was fragile and required innovative action. "The time is ripe to renew and redouble our efforts. Why should we allow the war in Darfur to last more than two years?"
Mr Pronk said he had asked the United Nations to send in 117 human rights observers and the AU hoped to soon deploy 150 of a promised 800 police officers.
But more help was quickly needed and possible options included police officers from the European Union, more AU peacekeepers, and a small civilian monitoring protection team similar to one now deployed in the south, he said.
John Danforth, the United States ambassador, backed Mr Pronk’s proposals. "I am for protecting the lives of the people of Darfur. I am for doing that on a very urgent basis," he said. "We must be focused on what practical steps can be taken."
About 1.7 million people are homeless and 70,000 are estimated to have died in Darfur, a region the UN says is one of the world’s worst humanitarian crises.
The conflict was sparked in 2003 when rebel groups took up arms against the government in a struggle over resources and power.
Khartoum retaliated by arming nomad militias known as the janjaweed who are now accused of murder, rape and arson.
At the UN Security Council’s urging, the AU has pledged to deploy more than 3,000 troops and monitors in Darfur, but to date has sent in only a third of these and says it needs more outside help to send more.
The US, which says genocide is taking place, wants the council to increase the pressure on the parties by imposing sanctions on their leaders. But some members, including Russia and China, oppose such punitive measures. Mr Pronk said sanctions, while still an option, should not be imposed now as Khartoum had just responded to international wishes by signing the peace agreement in the south ending the 21-year-long civil war.
A new incentive to work for peace in Darfur would now come from Western nations’ decision to withhold development aid until the Darfur crisis was resolved, he said.
But the parties must be made aware that "there is not much time left", Mr Pronk added.
"It is important for all parties in Darfur - the government and the rebels - to understand there is a limit to tolerance and ... sanctions are still something to be considered," Mr Danforth said.