Millennials are being squeezed out of the world's middle class as incomes stagnate and costs rise, according to research by the Organization for Economic Co-operation and Development (OECD).

In a report published Wednesday, the 36-nation intergovernmental economic body said younger people were struggling to make it into that bracket, while those who were already included were finding it difficult to maintain their position. It said it was due to deteriorating income growth coupled with increasing costs of housing and education.