The head of the UN refugee agency says the conflict in Sudan's Darfur region could have a devastating impact on the peace and security of the region.
The two-year-old African Union force in Darfur is overstretched
In a BBC interview, Antonio Guterres described Darfur as the "epicentre of a major earthquake".
Earlier UK PM Tony Blair urged Sudan's government to stop military action in the area and allow in a UN force.
The remarks come ahead of a day of action on Sunday to raise awareness of the region's plight.
In 2003, ethnic violence erupted between pro-government Arab militia and black Africans - who make up the majority of the region's population.
Since then, tens of thousands of people have died and as many as two million have been displaced
Mr Guterres said instability resulting from the Darfur conflict was spreading into Sudan's neighbours, Chad and the Central African Republic.
"I would say you must look at Darfur not only in itself, but as the epicentre of a major earthquake in the area that can have a devastating impact not only on peace and security but also terrible humanitarian consequences," he told the BBC.
The UN Security Council could not take action to introduce an international UN force unless Sudan gave its consent, which it was not yet prepared to do, the UN official said.
"The secretary-general is making huge efforts trying to create the conditions for this presence to finally be possible as a basic condition both for humanitarian action, for the protection of the people involved and also for a lasting peace to be possible," he said.
The remarks came as one of Sudan's vice-presidents, representing a former southern rebel movement currently sharing power in Khartoum, was quoted as saying he would accept a UN force.
First Vice President Salva Kiir Mayardit told the al-Sudani daily the government was incapable of protecting civilians in Darfur.
"The aggravation of the humanitarian and security situation in Darfur necessitates the intervention of international forces to protect civilians from the atrocities of the Janjaweed militias so long as the government is not capable of protecting them," he was quoted as saying.
Mr Blair said the Sudanese government should "live up to its obligations".
"I do not understand the government of Sudan's rejection of the UN force, or its threat to withdraw its welcome from the AU," he said.
Mr Blair pledged that Darfur would stay at the top of his agenda.
On Thursday, Oscar-winner George Clooney told the UN Security Council members that genocide was taking place in the region.