UNITED NATIONS — UN investigators arrived in Sudan to determine if genocide took place in Darfur and investigate reports of human rights violations in the war-torn province, a UN spokesman said Monday.

The UN mission in Sudan, meanwhile, is still being denied access to much of south Darfur and officials are concerned about the fate of thousands of displaced people who were kicked out of a major camp last week, spokesman Fred Eckhard said.

The team from the International Commission of Inquiry will travel to Darfur, in western Sudan, on Wednesday and stay until Nov. 20 to gather evidence, according to Eckhard. He said the team arrived in the Sudanese capital Khartoum on Sunday night.

The United States and some human rights groups have already claimed Sudan and Arab militia known as the Janjaweed are guilty of genocide in Darfur. UN Secretary-General Kofi Annan said in a report to the Security Council last week there are strong indications that war crimes and crimes against humanity were committed "on a large and systematic scale" in Darfur. Sudan also faces the threat of UN sanctions.

British Prime Minister Tony Blair on Monday also warned that Sudan must end the violence in Darfur or face action by the United Nations.

"There is a whole series of measures that have now been laid down for the Sudanese government to follow," Blair told the House of Commons. "If they don't follow them, there has to be a reference to the Security Council and necessary measures taken."

The United Nations has called Darfur the world's worst humanitarian crisis, saying the conflict there has claimed 70,000 lives since March -- mostly from disease and hunger -- and now affects 2 million people, up from 1.8 million in September.

Sudan is accused of backing the Janjaweed in its campaign of rapes, killings and the burning of villages, part of its effort to put down a rebellion by non-Arab African groups. The government denies backing the militia.

It wasn't immediately known how far the investigators would get because of the ban on UN travel in south Darfur.

That's the region where a camp called El Geer was destroyed last week and its residents forced to leave. Some have since returned but a UN-supplied water pump and generators there were looted.

The World Food Program said it has brought food to camps nearby and requested permission to distribute food to people who have gone back to El Geer.

The International Commission of Inquiry was established in response to a UN Security Council resolution in September. It is also charged with identifying those guilty of human rights violations and making sure they are held accountable.