"The issue is now fixed. The text is agreed," a diplomat from a Group of Eight (G8) member country told Reuters during a summit of the club of industrialised nations.
"The agreement within the G8 will follow the U.S. proposal to increase the aid for fighting these diseases to $60 billion in the forthcoming years with $30 billion coming from the U.S."
German Chancellor Angela Merkel will make the deal public on the summit's final day today, after a meeting with the heads of six African nations, including Nigeria's newly elected President Umaru Yar'Adua.
On Thursday, G8 leaders have agreed to seek "substantial" cuts in emissions in an effort to tackle climate change.
Previously, several aid agencies have said the G8 has betrayed Africa by not living up to the commitments made at Gleneagles.
"G8 leaders have just over 24 hours to restore faith in a promise that represents life or death for millions of people across the world," Stop Aids Campaign co-ordinator Steve Cockburn told Reuters news agency.
Celebrity campaigners such as rock stars Bono and Bob Geldof have been lobbying individual leaders at the summit, including German Chancellor Angela Merkel.
"The chancellor has asked us to trust her and we are tempted, but we cannot risk being let down by the G8 again," Bono said.
Nigerian President Umaru Yar'Adua told BBC News he would be seeking better trade deals for Africa and increased efforts to resolve the crisis in Darfur.
"We expect an increased partnership, increased share of free trade to African nations, an increased participation of the international community in resolving crises within the African continent - especially the Darfur crisis and the crisis in Somalia," he said.
