KHARTOUM, May 1 (Reuters) - The United Nations warned on Monday that the conflict in Sudan could force 800,000 people to flee the country as battles between rival military factions persisted in the capital despite a supposed ceasefire.

Hundreds of people have been killed and thousands wounded over 16 days of battles since disputes between the Sudanese army and the paramilitary Rapid Support Forces (RSF) erupted into conflict on April 15.

The crisis has unleashed a humanitarian disaster, damaged swathes of Khartoum, risked drawing in regional powers and reignited conflict in the Darfur region.

Many fear for their lives in the power struggle between the army chief and RSF head, who shared control of the government after a 2021 coup but fell out over a planned transition to civilian rule.

Both sides agreed on Sunday to extend a much-violated truce by 72 hours, and the U.N. told Reuters the rival forces may hold ceasefire talks in Saudi Arabia. But air strikes and artillery rang out on Monday as smoke hung over Khartoum and neighbouring cities.

U.N. official Raouf Mazou said the body's refugee agency was planning for an exodus of 815,000 people including 580,000 Sudanese as well as foreign refugees now living in the country. The country's population numbers 46 million.

Some 73,000 have already left Sudan, he said.

Egypt reported 40,000 Sudanese had crossed its border, and those who made the journey said conditions were arduous. Others have gone to Chad, South Sudan and Ethiopia, or sailed across the Red Sea to Saudi Arabia on evacuation boats.

At least 528 people have been killed and 4,599 wounded, the health ministry said. The United Nations has reported a similar number of dead but believes the real toll is much higher.