"It's worth pointing out that there is much that has been done," the prime minister said.
"When help is given, it does make a difference and there are health service systems and education systems that are being transformed and changed as a result of the help and commitment that has been given by the international community."
In addition to the former UN secretary general Mr Annan, the APP also includes Bob Geldof and is funded by Bill Gates.
Mr Geldof spoke at the event and was quoted by the Guardian as saying: "No one wants to see the compact of Gleneagles destroyed. Economic justice is the most sacred promise you can make, because if you break it you kill people.
"We cannot be the instruments of death - we need to be the instruments of life."
Britain is on track to meet its own pledges made at Gleneagles and Mr Blair noted that "far more" people were receiving treatment for HIV and Aids and education was reaching some African children for the first time.
But he concluded: "There are still far too many Africans who die when their death is preventable with our help."
The APP was established to focus world leaders' attention on the promises they made at Gleneagles and updating governments on the progress of targets which should be achieved by 2010.
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