Nairobi/Goma - Desperate civilians who fled a relentless rebel offensive in east Democratic Republic of Congo earlier this week were beginning to return home Friday as a fragile ceasefire continued to hold, an aid agency said.

Rebel Tutsi General Laurent Nkunda on Wednesday evening called a ceasefire as his troops were on the verge of taking the major city of Goma, the capital of North Kivu province.

Tens of thousands of people, many of them from the town of Kibumba, north of Goma, fled the advance as the Congolese army went into full retreat.

'Many people who fled Kibumba are now returning,' Clio van Cauter, a spokeswoman for Doctors Without Borders, told Deutsche Presse-Agentur dpa.

'Some are on their way home, others are waiting to find the means ... It is still too early to say whether that means they will stay at home,' she continued.

Fighting raged for four days and UN peacekeepers joined the battle, pounding Nkunda's National Congress for the Defence of the People (CNDP) with helicopter gunships.

UN peacekeepers were, however, stretched to the limit by the fighting and the UN's top envoy in DR Congo, Alan Doss, has called for more troops to add to the 17,000 contingent already in the sprawling Central African nation.

Many of those who fled are based in and around Goma, and aid agencies such as the Red Cross are warning that a humanitarian catastrophe is in the making unless urgent action is taken.

Congolese government troops who retreated to Goma, the capital of North Kivu province, have reportedly been looting and killing civilians.

Van Cauter said an outbreak of cholera had been confirmed in a camp north of Goma and there were fears it could spread rapidly.

The European Union on Thursday pledged 4 million euros in emergency aid for the displaced in the region.

Many aid agencies evacuated their staff from Goma on Wednesday as the rebels approached, but they now plan to take advantage of the ceasefire to return.

Charity World Vision said that its staff were planning on returning to the city on Saturday.

United Nations Secretary General Ban Ki-moon Friday urged Nkunda to stick to the ceasefire and said the situation was 'very threatening.'

Diplomatic efforts to resolve the crisis are also in full swing.

The top US envoy for Africa, Jendayi Frazer, arrived in the DR Congo on Thursday for talks with President Joseph Kabila aimed at ending the violence.

Frazer was also due to visit neighbouring Rwanda for talks with President Paul Kagame Friday.

French Foreign Minister Bernard Kouchner and British Foreign Secretary David Miliband were also planning on heading to Goma and Rwandan capital Kigali.

The EU's aid commissioner, Louis Michel, is also meeting with Kabila and Kagame in an attempt to get them to talk, something many believe is key to defusing tensions in the east of the DR Congo.

DR Congo has accused Rwanda of backing Nkunda and there were some reports of cross-border firing during the fighting. Nkunda says he is fighting to protect Tutsis from armed Hutu groups.

Many Hutus fled to Congo after the 1994 massacres in Rwanda when Hutu militants killed an estimated 800,000 Tutsis and moderate Hutus in the space of a few months.

The CNDP and other groups in January signed peace accords designed to end sporadic clashes that occurred during 2007, four years after a war that began in 1998 officially ended.

But the CNDP and government soldiers have been involved in repeated clashes in the eastern provinces of North and South Kivu since late August.

The UN said about 250,000 civilians have fled the fighting since August, bringing the number of refugees in North Kivu to almost 1 million.

More than 5 million people are estimated to have died as a result of the 1998-2003 war in the resource-rich nation, most of them from hunger and disease.

The conflict is often referred to as the African World War, owing to the large number of different armed forces involved.