UN Secretary-General Kofi Annan says current attempts to end the conflict in Sudan's Darfur region are not working.
Thousands have died in Darfur in recent months
He says the situation is deteriorating and the UN and Security Council urgently needs to reassess its actions.
The UN Security Council warned on Tuesday that it would consider a "full range of options" if the deteriorating security situation continues.
There are two existing UN resolutions threatening possible sanctions against the Sudanese authorities.
The UN has termed Darfur one of the world's worst humanitarian crises, with some two million refugees relying on aid handouts.
"A real reassessment" needs to be carried out by the UN and the Security Council "because quite frankly our approach is not working," said Mr Annan.
But he rejected US representative Steve Holliday's suggestion that he make another trip to the region.
"These kinds of decisions and actions have to be decided here and taken here, and so, whilst a trip to the region may some time be necessary, the reassessment is urgent," he said.
He said the millions who had been forced to flee their homes since the outbreak of violence in February 2003 were still suffering.
Thousands have died from illness and preventable diseases.
But aid agencies are unable to reach many of the most vulnerable because of the lack of security.
Mr Annan says urgent action is needed
The UK charity Save the Children has withdrawn from Darfur after four of their staff were killed, and Medicins San Frontieres (MSF) expressed shock at the killing of one of its workers.
Mr Annan said the African Union has not been able to deploy as many peacekeeping forces in Darfur as hoped, and they needed desperate help.
The force currently stands at less than a quarter of the projected number of 4,000 troops.
The UN Security Council has imposed an arms embargo against non-government groups and individuals including the pro-government Janjaweed militia.
It has also threatened oil sanctions unless the violence ends.
Aid agencies want the embargo extended to the government as well as the imposition of travel sanctions and freezing the assets of individuals.
But the council has little room for manoeuvre, says the BBC's Susannah Price at the UN in New York.
China and Russia, which have a veto on the council, oppose sanctions. The US, which also has a veto, does not want to refer the suspected war crimes cases to the International Criminal Court.