By Susannah Price
BBC correspondent at the United Nations
UN Secretary General Kofi Annan has said he will meet US Secretary of State Colin Powell in Sudan next week to discuss the Darfur conflict.
Annan says sanctions are one of the possible options
Mr Annan urged the world community to act immediately to stop what he called the catastrophe in western Sudan.
He said both he and Mr Powell would be pressuring the Sudanese government to carry out its obligations.
Human rights groups accuse Khartoum of backing Arab militia groups that have killed thousands of Africans in Darfur.
The fighting has driven more than a million people from their homes.
Mr Annan said he was going to Darfur to see the situation for himself and to put additional pressure on the government.
He said terrible crimes and serious human rights violations had been committed against the people there.
Mr Annan stopped short of blaming the Sudanese government directly for the violence and said it had to disarm the militias, protect the people and allow them to go home.
He said that both he and Mr Powell would be pressuring the Sudanese government to deal with the humanitarian crisis, and if it could not protect the population, the international community should be prepared to assist.
The UN Security Council earlier this month passed a resolution calling for all sides to play their part in ending the fighting.
Mr Annan said the time may come for the Council to take stronger action.
"If it became necessary to take action, the Council will have to decide what to do. Someone has suggested sanctions, there are also a series of actions the Council can take and it will be up to them to decide," he said.
"We have had other situations where the government concerned has failed to protect its people and the international community has gone in to help."
Mr Annan said humanitarian relief for the people of Darfur was now the most urgent need and he warned hundreds of thousands of lives were at stake.
Food is running short for Darfur's refugees
He expressed concern there were still problems getting supplies into Darfur and delays in granting visas for humanitarian workers.
He said complex conflicts over land and other issues lay behind the atrocities and they needed to be solved urgently.
Mr Annan will also visit refugees from Darfur over the border in Chad and will discuss the crisis at the African Union summit in Ethiopia.