(Adds riots in Goma on Sunday)

By Joe Bavier

KINSHASA, Sept 22 (Reuters) - Weeks of heavy fighting between the army and Tutsi rebels in eastern Congo's North Kivu province has forced 100,000 people from their homes, the United Nations said on Monday.

Congolese forces and rebels led by renegade Tutsi General Laurent Nkunda started their latest bout of fighting in late August when a January peace deal aimed at ending more than a decade of violence collapsed.

On Monday the army blasted Nkunda's hilltop positions with rockets, heavy guns, and helicopter gunships.

U.N. and other international mediators have urged all sides to pull back to initial positions and return to talks, but with little effect. Frustration that these calls were being ignored spilled over into anger among many locals, triggering riots and looting in the provincial capital Goma on Sunday.

"We estimate that around 100,000 people have been displaced since the renewed fighting started on Aug. 28," Christophe Illemassene, spokesman for the U.N. humanitarian coordination office, OCHA, said.

North Kivu is one of the world's worst conflict-driven humanitarian crises. An estimated 5.4 million have died from fighting, hunger and disease since a five-year war, fuelled by Congo's mineral riches, started in 1998.

The latest wave of clashes is worsening an already dire humanitarian crisis in the tiny border province.

More than 830,000 North Kivu people had already fled on-off fighting last year and sporadic clashes during this year's eight-month peace process, which was plagued from the start by daily ceasefire violations.

Illemassene said many of those recently displaced had already been forced to flee several times, and it was unclear how many were new internal refugees.

The daily fighting is also hampering aid efforts.

"Delivery of assistance is being limited, because of the lack of access," he said. "It's definitely a concern, the humanitarian situation. We're very concerned."

The U.N. mission in Congo has come under pressure from local officials and the government for not doing enough to pressure Nkunda's rebels to disband and reintegrate into the army.

The transfer of bodies of government soldiers to a hospital in Goma on Sunday sparked angry anti-rebel protests that degenerated into riots and looting, U.N. officials said.

A mob, led by the widows of the dead soldiers, attacked petrol stations rumoured to be owned by Nkunda.

Peacekeepers fired in the air to repel an angry crowd trying to force its way into a U.N. base on the outskirts of the city.

The U.N. mission cancelled flights from the capital Kinshasa to Goma on Monday and restricted its employees' movements there.

"We've asked our personnel to move about only if it is absolutely necessary," Lieutenant-Colonel Jean-Paul Dietrich, the U.N. mission's military spokesman, told Reuters. (Editing by Alistair Thomson and Matthew Jones)

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