(Updates with details, quotes, background)
By Hez Holland
KIBATI, Congo, Nov 3 (Reuters) - A U.N. convoy carrying aid workers and medical supplies, escorted by U.N. troops, crossed into a rebel-held zone of eastern Congo on Monday on a mission to help tens of thousands of civilians displaced by fighting.
The convoy of a dozen all-terrain vehicles and two truckloads of U.N. peacekeepers rolled through the front line separating Congolese army troops and Tutsi rebels, whose offensive last week triggered a humanitarian emergency.
The relief caravan, which was also carrying water and sanitation equipment, is heading through Democratic Republic of Congo's North Kivu province to Rutshuru, a town captured last week by rebels loyal to renegade Tutsi General Laurent Nkunda.
U.N. agencies and humanitarian NGOs launched the coordinated mission as African and Western governments sought to organise a regional summit this week to bring together the presidents of Congo and Rwanda to discuss the conflict on their common border.
Rebel chief Nkunda has declared a ceasefire, which is holding, but aid agencies have called the humanitarian situation "catastrophic" and say that tens of thousands of civilians are in urgent need of shelter, food, water and medical care.
Sean Raster, a logistician of the British medical charity Merlin, said the convoy would make a preliminary assessment of medical and other emergency needs in the Rutshuru area.
"We want to look at the security situation and gradually introduce our programmes," he told Reuters on the convoy.
The U.N. refugee agency UNHCR has said it feared that at least 50,000 displaced civilians may have abandoned unprotected camps around Rutshuru, which is 70 km (45 miles) north of the North Kivu provincial capital Goma.
The refugees are thought to be roaming the bush, seeking shelter after fleeing attacks by Nkunda's Tutsi fighters and killings, lootings and rapes by renegade army soldiers.
European, U.S. and U.N. envoys have criss-crossed the Great Lakes region in recent days, trying to prevent the newly resurgent Tutsi rebellion in the eastern Congolese borderlands from escalating into a rerun of Congo's 1998-2003 war.
After a weekend diplomatic shuttle that took them to Congo, Rwanda and Tanzania, the French and British foreign ministers called for more international aid to Congo's North Kivu.
But Bernard Kouchner and David Miliband stopped short of announcing a deployment of European Union troops to Congo.
SECURITY "CRITICAL"
France, which holds the rotating EU presidency, had mooted the proposal but encountered resistance from some member states.
The EU ministers recommended reinforcing the 17,000-strong U.N. peacekeeping force in Congo, already the world's biggest but badly stretched across a nation the size of Western Europe.
"The critical thing obviously is to improve the security. There are 17,000 U.N. troops in the Democratic Republic of Congo, about 5,000 in the key province in the east ... and they are providing protection for the aid to get to the distressed people on the DRC-Rwanda border," Miliband told BBC Radio.
East Congolese refugees have complained the U.N. force does not protect them and they have even attacked peacekeepers.
Miliband said: "We also have to recognise that without a political settlement there is never going to be any progress."
He recommended that Congolese President Joseph Kabila and Rwandan President Paul Kagame work to build a lasting east Congo peace settlement on the basis of previous accords made.
Tanzanian President and African Union chairman Jakaya Kikwete and AU Commission chief Jean Ping have proposed a regional summit on east Congo, possibly this week in Nairobi.
An estimated one million people have been forced from their homes in North Kivu by two years of violence that has persisted despite the end of the 1998-2003 war in the vast, former Belgian colony, which is rich in copper, cobalt, gold and diamonds.
Nkunda, who says his four-year-old bush rebellion aims to defend east Congolese Tutsis, has offered to talk to the government but wants a neutral mediator.
He accuses Kabila's army of backing Rwandan Hutu rebels operating in east Congo who took part in the 1994 genocide killings in Rwanda of 800,000 Tutsis and moderate Hutus.
Kabila's government denies this and has in turn accused Tutsi-led Rwanda of backing Nkunda, a charge denied by Kigali.