The world's leading nations have not kept their promises on foreign aid, David Cameron has said.
Speaking at the G8 summit in France, the UK prime minister said there was a $19bn gap between what had been pledged and what had been delivered.
He vowed to be "tough" on world leaders over the issue and to continue to make the argument to the British people that foreign aid was vital to UK interests.
"The UK will not balance its books on the backs of the poorest," he said.
He was speaking after the UK pledged £110m in additional support for Egypt and Tunisia as part of a £20bn package of economic aid for countries in North Africa which have embraced political reform in the "Arab Spring" uprisings.
Before last year's UK general election all the main parties agreed that international aid should rise to 0.7% of gross national income by 2013.
But some Conservative MPs have questioned why the government is increasing foreign aid spending when most domestic budgets are being cut.
Backbencher Philip Davies told the Mail: "Once again we are the soft touch of the international community. We keep on spending money on foreign aid when we haven't got any money to spend on people at home.
"Every other country has accepted that spending money at home is better than spending money abroad."
The prime minister acknowledged the issue was "controversial" but said he believed it was a "moral principle" to help the world's poorest and was also in the UK's interest as it helped prevent wider instability and conflict.
'These things matter'
He said the UK would be the first country to fulfil the internationally agreed target for countries to spend 0.7% of their income on foreign aid by 2013.
"Britain will keep its promises and I was tough in urging my counterparts to do the same," he said. "The reality is that as a whole the G8 has not."
He added: "I cannot guarantee that the Italians or the Germans, or whoever else, will meet the promises they make.
"But I'll tell you what I think. I think what people back at home think about these summits is that frankly a bunch of people in suits get together and make some promises, particularly to the world's poorest, and then they go in and have a big lunch and forget all about the promises. I am not prepared to do that."
Recalling where he was when he watched the Live Aid concerts in 1985 and the Live8 events in 2005 - which were followed by substantial aid pledges at the G8 summit in Gleneagles - Mr Cameron said he would continue to make the case for foreign aid, even if it proved unpopular at home.
"These things matter," he added.
"If we are going to get across to the poorest people in the world that we care about their plight and we want them to join one world with the rest of us, we have to make promises and keep promises.
"Of course it is difficult when we are having to make difficult decisions at home. But I don't believe 0.7% of our gross national income is too high a price to pay in terms of saving lives of the poorest people in the poorest countries."
In their declaration at the end of the two-day summit, G8 leaders - including US President Barack Obama and French President Nicolas Sarkozy - said their nations were "strongly committed" to meeting overseas aid commitments.
But development charity World Vision said their record was not encouraging.
"The UK has led while the rest of the G8 has responded with words and no action," said its spokesman Chris Page