(Adds U.N. Security Council, US State Department comments)

By Hez Holland

GOMA, Congo, Oct 28 (Reuters) - Congolese Tutsi rebels overran the eastern town of Rutshuru on Tuesday, a rebel spokesman said, forcing tens of thousands of people to flee.

The rebels loyal to renegade General Laurent Nkunda had also encircled the provincial capital Goma, 100 km (60 miles) to the south, the rebel spokesman said. That could not be independently verified.

"We have taken the town of Rutshuru and the (adjoining) town of Kiwanja," Bertrand Bisimwa of the rebel National Congress for the Defence of the People, told Reuters.

The U.N peacekeeping mission in Congo, known as MONUC, said rebels were in Rutshuru, but that peacekeeping forces were also in the town and there was no fighting.

"MONUC confirms CNDP presence in the town of Rutshuru," said spokesman Michel Bonnardeaux. "We are there to protect the civilian population despite the fact that the FARDC (Congolese army) has fled the area."

Earlier the head of the Congo's army operations in the area, Colonel Delphin Kahimbi, said he would have to abandon the town in the face of a rebel advance that began on Sunday.

The U.N. Security Council, which is considering a request from the peacekeepers to beef up its forces, issued a statement strongly condemning the rebel offensive and calling for a ceasefire.

U.N. peacekeepers had to scrap a bid to evacuate around 50 foreign aid workers from Rutshuru, in North Kivu province.

"The situation is very tense. They were blocked by both the population and soldiers. There are also attacks on humanitarian installations and looting," said Evo Brandau, spokesman for the U.N. humanitarian office. "The army is no longer guaranteeing security."

The provinces of North and South Kivu are home to the majority of Congo's tin ore deposits, but most foreign investment is concentrated on Katanga, the copper-mining province in the southeast of the country.

Rutshuru normally shelters tens of thousands of internal refugees displaced by nearly two years of sporadic fighting, but Kahimbi said the camps had emptied.

REFUGEES FLEE AGAIN

The United States called for an end to the "deplorable violence.

"The United States is deeply concerned by the worsening humanitarian situation in the eastern provinces of the Democratic Republic of the Congo," State Department spokesman Sean McCormack said in a statement issued in Washington.

The U.N. refugee agency UNHCR said it was preparing for the arrival of 30,000 people at its Kibati camp 10 km (6 miles) north of Goma, including 20,000 from the village of Kibumba, 20 km (12 miles) from Goma, which insurgents attacked on Monday.

Also on Monday, peacekeepers' helicopters attacked rebel positions north of Goma, drawing anti-aircraft fire from Nkunda loyalists.

"MONUC will use all available means to protect urban centers including Rutshuru, Sake (west of Goma), and Goma," said Bonnardeaux of the peacekeeping force, whose 17,000 personnel are mostly deployed in Congo's east.

Nkunda's rebels accuse Congo's army of collaborating with the Democratic Forces for the Liberation of Rwanda, which includes Hutu militias and former Rwandan soldiers responsible for Rwanda's 1994 genocide of Tutsis and moderate Hutus.

About 250,000 civilians have fled their homes in North Kivu since a January peace deal collapsed in August. Nearly two years of clashes had already displaced around 850,000 people before the latest fighting began, according to U.N. figures.

Congo's 1998-2003 war and the resulting humanitarian crisis have killed an estimated 5.4 million people.

The U.N. Security Council, in a statement read by its president Zhang Yesui of China, expressed "grave concern" at the fighting and "strongly condemned the offensive operations." It called for an immediate ceasefire by all parties.

U.N. peace-keeping chief Alain Le Roy, who briefed the council, told reporters there was now an increasing sense of urgency over a request earlier this month for reinforcements.

MONUC chief Alan Doss said he was seeking two extra light infantry battalions and specialized forces.

"We will see what will be out of it but clearly the request ... has been heard clearly by all member states," Le Roy said.

But France's U.N. Ambassador Jean-Maurice Ripert said this would take time. "For the moment the important thing is to be sure that MONUC is in a position to resist with the means it has," he told journalists.

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