Tongo, Congo ? Tutsi-led rebels tightened their hold on newly seized swaths of eastern Congo on Saturday, forcing tens of thousands of frightened, rain-soaked civilians out of makeshift refugee camps and stopping some from fleeing to government-held territory.

Aid organizations said they were increasingly worried about a lack of food and shelter.

European officials offered sympathy but no concrete promise of military reinforcements for the Congolese troops and U.N. peacekeepers routed by rebel forces in the sudden and dramatic escalation of eastern Congo’s civil war in the past week.

The rebels appeared to be maintaining a unilateral cease-fire they declared a day earlier, focusing on consolidating territories that stretch to the doorstep of the provincial capital, Goma, instead of taking the city.

The rebels, who said people were leaving the refugee camps of their own free will, asserted that they stopped short of Goma in hopes of stopping the chaos that had engulfed it as government troops fled along with tens of thousands of refugees. However, Goma was also the site of rebel leader Laurent Nkunda’s greatest defeat when U.N. attack helicopters fired on his fighters advancing on the city in December, killing hundreds of them. It was not clear if that experience influenced his decision.

The area that Nkunda has seized is a minerally and agriculturally rich area that commands much of the access to the Rwandan and Ugandan borders.

Britain’s minister for Africa said the U.K. could send troops if Nkunda’s cease-fire fails but the first reinforcements should be soldiers deployed elsewhere in the country with the U.N. force known by its French acronym, MONUC.

British Foreign Minister David Miliband, who rushed to the region with French Foreign Minister Bernard Kouchner after the outbreak of fighting, downplayed the possibility of an EU peacekeeping force.

“Nothing is being ruled out, and that remains the point,” he told reporters in the Rwandan capital after leaving a refugee camp outside Goma. “But we have a 17,000-strong MONUC force, and that is of course the first call for security support in the Congo.”

Kouchner said his government was committed to humanitarian assistance, but not necessarily sending in troops.

The French aid group Doctors Without Borders said it was “extremely concerned about the tens of thousands of people currently on the move, fleeing the fighting.” It said they were in “urgent need of clean water, basic items like blankets and shelter materials, and food.”

Dozens of people already have died of cholera or severe diarrhea for lack of clean water.

Nkunda told the AP by telephone on Saturday that he has opened a humanitarian corridor to allow refugees to come home and for aid to get through.

But there was no sign of any food getting through Saturday, with aid workers saying some contractors are refusing to move food because of the insecurity.