(Adds Security Council president's statement)

By Claudia Parsons

UNITED NATIONS, Dec 12 (Reuters) - U.N. Secretary-General Ban Ki-moon urged the Congolese government on Wednesday to protect civilians endangered by an offensive against Tutsi rebels and he urged the rebels to lay down their arms.

Ban's spokeswoman Marie Okabe said an estimated 60,000 to 70,000 people already displaced by violence were reported to be on the move again this week because of renewed fighting in the eastern province of North Kivu.

President Joseph Kabila threw more than 20,000 soldiers into a major campaign on Dec. 3 to snuff out renegade Tutsi Gen. Laurent Nkunda's 3-year-old rebellion, which draws on some 4,000 disciplined and battle-hardened Tutsi fighters.

"The secretary-general is deeply concerned about the intense fighting in North Kivu in recent days which has caused further suffering of the civilian population," his office said in a statement. "He is particularly troubled by reports of massive displacement and mistreatment of the population."

The army, which is getting logistical support from the U.N. peacekeeping mission known as MONUC, initially made rapid gains in a two-pronged offensive before meeting dogged resistance in the rugged hills on the threshold of Nkunda's fiefdom.

The statement said the United Nations, through MONUC, supported the government effort to establish its authority over the rebels in the east of the Democratic Republic of Congo.

"The secretary-general calls on the government of the DRC to take all measures necessary to protect civilians," it said.

"The secretary-general calls on the forces of Laurent Nkunda to lay down their arms," it added.

The U.N. Security Council was briefed on the fighting on Wednesday, council president Marcello Spatafora said.

"Members of the council expressed their serious concern at the humanitarian consequence of the recent fighting," he told reporters, adding that the council noted the "primary responsibility" of the government to protect civilians.

Okabe said civilians were fleeing from refugee camps towards the provincial capital, Goma, and that the children's agency UNICEF and the World Food Program were distributing supplies and food despite reduced access to conflict zones.

She said the United Nations was particularly concerned about reports of rapes in North Kivu, where she said there had been 2,700 cases of rape reported between January and October. (Editing by Cynthia Osterman and Todd Eastham)

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