The US meanwhile suspended talks on normalisation of relations with Sudan, blaming leaders from the north and south of the country for the violence.
Richard Williamson, the US special envoy to Sudan, said: "At this point the leadership of either side is not interested in meaningful peace.
"I won't be part of a sham peace that won't change the situation," he said, announcing the suspension of talks.
Williamson's comments came amid an increasing crisis in Sudan after clashes between the north and south in the oil-rich district of Abyei last month and an attack on the capital, Khartoum, by JEM.
Somalia is also facing continuing instability despite UN-brokered talks being held in Djibouti.
The UN says that up to 300,000 people have died and more than 2.2 million have fled their homes since the Darfur conflict broke out in February 2003.
The Sudanese government says that about 10,000 have been killed.
Jan Eliasson, the UN envoy to Darfur, has warned that the conflict in Darfur is deteriorating due to a breakdown in relations between Sudan and Chad after a rebel attack on the capital, Ndjamena, and the JEM assault on Khartoum.
|"... the JEM have decided ... |
to end the suffering of this province in 2008, whether through peace or war"
Khalil Ibrahim, Justice and Equality Movement leader
Ibrahim told Al Jazeera that the movement had resolved to settle the issue of Darfur by the end of the year, either through negotiation or conflict.
"We now face a real crisis and ongoing death threats," he said.
"We, the JEM, have decided, during our conference, to end the suffering of this province in 2008, whether through peace or war."
However, UN mediators have been forced to postpone a meeting planned to address the situation after Ibrahim's JEM and the Sudanese Liberation Movement objected to other rebel groups attending.
"We had planned it so concretely that we actually had a place and time in Switzerland, but we were unfortunately prevented from starting this week as planned," Eliasson told reporters in Khartoum on Monday.
Eliasson expressed his concern at last month's fighting between the north and the south which left the Abyei district devastated and up to 90,000 displaced.
"Since the end of last year, things have gone in the wrong direction," he said.
"If there is an escalation at this stage and at the same time the rainy season starts, we may enter a catastrophic situation."
Williamson has been attempting to resolve the crisis, but on Monday he said that talks with the National Congress party of Omar al-Bashir, the president, and the former rebel Sudan People's Liberation Movement had proved fruitless.
"I have tried to help both of them think through what's in their interest and it's clearly in both of their interests to defuse this situation which continues to be explosive.
"It's key to take steps so that the Abyei situation doesn't remain a powder keg where this type of violence and destruction can happen."
Sudanese government forces control the main town in the Abyei district after two bouts of heavy fighting ended on May 20.
Abyei, which sits on an estimated half a billion dollars of oil, was accorded a special status and was to be governed by a joint administration until twin referendums in 2011.
They will decide whether it remains part of the north or joins the south, as well as whether the south will secede.
The UN has warned that the violence could destroy the peace deal signed between the north and south in 2005 that ended Africa's longest-running civil war.