Kinshasa — U.N. attack helicopters targeted M23 rebels in eastern Congo on Saturday after fighting resumed following a months-long lull in violence, a local official said.

"MONUSCO helicopters this morning bombarded the M23 positions in the city of Kibumba," said North Kivu governor Julien Paluku. He said the Congolese army had earlier retreated from Kibumba, which is 30 kilometers north of Goma, after thousands of Rwandans, who he says were backing the rebels, attacked early Saturday.

"The fighting was very violent between the Congolese military and the M23 rebels back by the Rwandan army," he said. "Rwandan forces bombarded our positions in Kibumba since early this morning and an estimated 3,500 crossed the border to attack us."

Rwanda rejected the accusations, the latest in a string of charges by Kinshasa, and called on both the army and the rebels to halt the fighting as shells were landing in its territory.

More than five million people are estimated to have died from violence, hunger and disease in wars in Congo since 1998. It is the deadliest conflict since World War Two.

United Nations experts say they have evidence of Rwanda's rebel support and want the U.N. Security Council to impose sanctions on Rwandan officials as a result.