International donors have pledged an extra $200m (£110m) for peacekeeping in Sudan's strife-torn Darfur region.
AU troops are due to be reinforced in coming months
The African Union (AU) has 2,300 troops on the ground and is asking for cash and equipment to build up its force.
UN Secretary-General Kofi Annan told a donor conference in Ethiopia that an epic relief effort would be needed if the conflict was not stopped.
More than 180,000 people have died in Darfur, and some two million have been forced from their homes.
Delegations from the European Union, the US and Nato are among those attending the conference.
Mr Annan, who is chairing the conference, is expected to travel on from Ethiopia to meet Sudanese leaders in Khartoum and to go from there to Darfur itself.
"We are running a race against time," he told delegates.
"If violence and fear prevent the people of Darfur from planting and growing crops next year, then millions will have to be sustained by an epic relief effort which will stretch international capacity to the maximum."
He urged rich countries not to delay with funding an expansion of the force.
"An expanded African mission, at full operational capacity, will mean the great majority of vulnerable civilians in Darfur will be protected from violence," he said.
Canada responded with a pledge of $134m, while the US added another $50m to $95m already offered.
The UK pledged another $12m, and smaller contributions came from France and Germany.
Nato and the EU have already promised logistical support.
Speaking on the BBC's Today programme, Nato Secretary General Jaap de Hoop Scheffer said the first item on the agenda was airlifts.
But he dismissed calls for Nato to get directly involved with peacekeeping, in the absence of a mandate from the UN Security Council.
In all, the AU says it could increase its force to 7,700 by September and more than 12,000 next year. It says it needs $723m but was still $350m short at the start of the conference.
Mission 'in jeopardy'
Just before the meeting, the UN's special envoy on Darfur, Jan Pronk, accused the rebels of refusing to co-operate with the AU force.
AFRICAN UNION REQUESTS
116 armoured personnel carriers
24 armoured ambulances
16 helicopters, including 6 gunships
7 heavy lift cargo aircraft
Other vehicles including trucks and cars
Communications equipment and office supplies
Basic equipment such as tents, stoves and flak jackets
The Sudanese government has been frequently criticised for blocking aid shipments and interfering with peacekeeping, as well as for its refusal to comply with the ceasefire triggering a breakdown of pace talks late last year.
The peace talks are due to restart in Nigeria on 10 June.
Things are not getting much worse in Darfur, but they are not getting better either, says the BBC's Jonah Fisher in Khartoum.
In the last four months there have been no major confrontations between the government and rebel movements, but violence against displaced people and attacks on aid vehicles have continued.
"The situation remains unacceptable. Civilians are still at risk and subject to attacks... Violence is increasingly targeted at aid workers, hampering their difficult work," Mr Annan said on Thursday, adding that where the AU was deployed, attacks did not happen.