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By John Acher and Wojciech Moskwa

OSLO, May 7 (Reuters) - Donor nations pledged a preliminary $4.8 billion in assistance to Sudan on Wednesday to bolster a fragile 2005 north-south peace in Africa's biggest country that is still torn by violence in its western Darfur province.

Sudan had said it needed $6.1 billion up to 2011, on top of $2 billion in humanitarian aid.

A deadly aerial bombing in Darfur three days ago cast a shadow over the Oslo conference and some delegates said it made countries reluctant to pledge openly before a satisfactory explanation.

"This conference is a big success," Luka Biong Deng, minister for presidential affairs for semi-autonomous south Sudan told Reuters. "The international community confirmed it is firm on bringing peace to Sudan, sustaining the peace and giving a peace dividend to its people."

The funds will be split between humanitarian efforts and longer-term development aid favoured by Sudan as it seeks to keep its people behind the 2005 comprehensive peace agreement (CPA), which ended the longest civil war in Africa.

"The implementation of the CPA is more critical than ever. The CPA will benefit not only the Sudanese, it will have ripple effects throughout the region," said senior World Bank official Hartwig Schafer after announcing the pledged total.

Diplomats at the conference condemned Sunday's government bombing attack on a school and marketplace in Darfur, which killed 12 including six children.

International experts estimate 200,000 have died and 2.5 million have been driven from their homes in five years of revolt in Darfur. Sudan puts the death toll at about 10,000.

"The international community cannot make peace in Sudan," said Aid Minister Erik Solheim of host nation Norway which pledged $500 million. "Peace must be home-grown, and then we can give support in many ways."

DARFUR LOOMS LARGE

"The extent to which these funds can be used for development will depend crucially on resolution of the Darfur crisis," said Dave Fish, head of the British delegation which pledged $650 million, second only to the United States' $1.6 billion.

Washington also aims to spend nearly $2 billion on peacekeeping in Sudan this year and next, a U.S. diplomat said.

Sudanese officials said the bombing highlighted the fluid security situation and the need to push through the CPA, which includes plans to hold elections in 2009.

"Stability and peace is indivisible," Sudan's Vice President Ali Osman Taha told the conference.

"The need for a comprehensive ceasefire cannot be more emphasised than by the bombardment that took place a few days ago," Taha said.

Ashraf Qazi, special representative of the U.N. Secretary General for Sudan, said: "(This) has indeed been a success. While CPA implementation has fallen behind schedule, the fact is that it remains on track and your contribution will help."

Katherine Almquist of Washington's aid arm USAid urged Sudan to push ahead with its election law and ensure that Darfur was included in the ballot to give it a national character.

"We strongly hope this will move forward with all due haste," she said. Sudan officials vowed that the ballot would be held and an election law sent to the national assembly "soon". (Editing by Matthew Jones) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/)

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