United Nations Secretary General Ban Ki-moon has arrived in Sudan to press for an end to the violence in the western province of Darfur.
More than two million people have been displaced by the fighting
The conflict has claimed 200,000 lives and left millions displaced.
Mr Ban, who will visit a Darfur refugee camp on Wednesday, has said the priority is to get a 26,000-strong UN and African Union force into position.
The new troops are not due to arrive until next year but violence continues, with hundreds killed in August.
African countries have offered the troops but Western nations have been slow to come up with the logistical support and the attack helicopters needed for such a massive peacekeeping operation, says the BBC's Laura Trevelyan, who is travelling with Mr Ban.
Mr Ban is also trying to encourage peace talks between the Sudanese government and the many rebel groups.
He will meet Sudanese President Omar al-Bashir and also visit neighbouring Chad and Libya, where leader Muammar Gaddafi has played a role in bringing Darfur rebels to negotiations.
Our correspondent says the secretary general wants to see for himself the plight of the people of Darfur and understand the difficult conditions into which the world's biggest peacekeeping force will eventually be deployed.
This visit will be a delicate balancing act for Mr Ban, who has made Darfur his top priority, she adds.
He wants to encourage the Sudanese government, who have finally accepted peacekeepers, while condemning the killings and getting political talks going.
Last week he outlined a three-point plan for the region, involving the peacekeeping operation, peace talks and aid.
But UN officials have tried to play down the tour.
"This is not a trip about breakthroughs. We're not at a breakthrough stage," an unnamed official told Reuters news agency.