KHARTOUM (Reuters) -Clashes between rival military factions could be heard overnight in parts of Sudan's capital, residents said on Wednesday, the second full day of a week-long ceasefire designed to allow for the delivery of aid and lay the ground for a more lasting truce.

The ceasefire, which is being monitored by Saudi Arabia and the United States as well as the warring parties, comes after five weeks of intensive warfare in the capital Khartoum and outbursts of violence in other areas of the country, including the western region of Darfur.

Residents of Omdurman, one of the three cities around the confluence of the Blue Nile and White Nile rivers that make up Sudan's greater capital, said there had been exchanges of fire late on Tuesday in several areas.

Heavy artillery fire could be heard near the Wadi Sayidna military base on the outskirts of the capital, they said.

"We heard the sound of heavy clashes yesterday night in north Omdurman but the situation is better after the truce. Every day we have hope in the possibility that the nightmare of the war ends," Hassan Awad, a 48-year-old university professor, told Reuters by phone.

The ceasefire brought a relative lull in fighting in Khartoum earlier on Tuesday, though there has so far been little sign of a rapid scale-up in humanitarian relief, with aid workers saying that many of the supplies and staff arriving at Port Sudan on the Red Sea coast have been awaiting security permits and guarantees.

The fighting pits Sudan's army against the powerful paramilitary Rapid Support Forces (RSF), and erupted as plans for a internationally-backed political transition towards elections under a civilian government were set to be finalised.

Sudan was facing severe humanitarian pressures even before the conflict broke out on April 15, forcing more than 1.1 million people to flee their homes and threatening to destabilise the region.

More than 300,000 people have now fled Sudan to neighbouring countries, with many crossing into Chad and Egypt in the last few days, Filippo Grandi, head of the U.N. refugee agency, said on Wednesday.

"Donor contributions to the refugee response plan remain scarce. We need more resources, urgently, to support countries hosting refugees," he said in a Tweet.

The U.N. says that the number of people requiring aid within Sudan has jumped to 25 million, more than half the population.

(Reporting by Khalid Abdelaziz in DubaiWriting by Aidan LewisEditing by Christina Fincher)