Donor money that comes with strings attached cuts the value of aid to recipient countries 25-40 percent, because it obliges them to purchase uncompetitively priced imports from the richer nations, says a new UN study on African economies.

The 24-page study singles out four countries - Norway, Denmark, the Netherlands and the United Kingdom - as the only donors breaking away from the concept of ''tied aid'', which comes with strings attached.

The four nations now provide more than 90 percent of aid "untied", says the report, which will go before the current session of the UN Economic and Social Council (ECOSOC), scheduled to end July 23.