A review of international aid is expected to remove 16 countries - including Angola, Vietnam and Cambodia - from the list of those which receive direct help from Britain.
Aid charities have raised concerns that the countries which will continue to get support, such as Afghanistan and Somalia, have been chosen because they are considered vital to maintaining UK security.
World Development Movement head of policy Julian Oram told the BBC Radio 4 Today programme: "What we are concerned about is the focus on a smaller number of countries, which actually takes money away from some of the world's poorest countries, like Niger, Angola and Cambodia and channels it into countries where there is deemed to be a higher security risk to the UK."
But Mr Mitchell responded: "In terms of the suggestion that we are securitising aid, we are dealing with parts of the world where people are doubly cursed - not only because they live in extreme poverty but also because they live in very conflicted societies."
The Government has committed the UK to meeting the United Nations target of spending 0.7% of GDP on aid by 2013. Total assistance is due to rise from £7 billion to £11 billion by 2015.
But ministers face criticism for merely freezing funding for India - which can afford its own space programme - at £280 million a year for the next four years.
Asked about the extent of overseas aid at a time of spending cuts at home, Mr Mitchell told BBC Breakfast: "We are dealing with a scale of poverty here around the world of a completely different order.
"And we do it because it's morally right, it's about our values as a country and as a Government, and also because it's in our national interest."
On India, he added: "We are walking the last mile with India in terms of its development programme."